The walkthrough writers give a good description on completing the level:
Take out the two sentry droids and then have Finn melt the circular line at the back with his lightsaber. Then pull on the grapple on the crate next to it. Build the resulting debris into a laser cannon thing and jump on the back of it. Have Chewie throw a thermal at the shiny metal barrier revealed. Shimmy across the gap and have Finn and Han pull on the two grapples. Build the ladder, head up as Chewie and pull on the handles. Hop across the handles and deal with the troopers. Rebuild the debris in the middle to reveal two targets. Shoot both, and head up the revealed vertical jump as Finn. Rebuild the object to the right to fire a rope off to the right. Jump up to it to automatically zipline over to the right. Head left and use your lightsaber on the red object near the barrier to get everyone through. Blow up the metal satellite dish at the right end of the area using Chewie's thermals. Multi-build left and press the switch. Quickly destroy the multi-build and rebuild it top-centre before the power moves too far along. Have Finn access the First Order panel and solve the matchmaking puzzle. Head into the elevator.
If you end up destroying all five sentry droids in this first part of the level - highly likely, as they're attacking you - you'll end up with one of the minikits described on the next page.
Sneak all the way right until you get to the green smoke, and have Finn walk through it. After the turret is activated, jump off to the left to the lower platform. Deal with the two troopers and smash the objects in the foreground. Pick up the yellow wheel, attach it to the pipes and rotate it. Chewie can then sneak down the stairs left of the turret, smash the object in front of the orange handles and then pull them. Build a mini-snowspeeder from the debris to deal with the turret. Send Han across the gap using the grapple and scan the object above and to the left of the scan area. A target should be revealed, shoot it. Get everyone over the ice bridge and then Han and Finn can pull the grapples over the red barrier to the right. Once the barrier is off Chewie can throw a thermal. Deal with the troopers on the far side of the door and have Finn unlock the First Order terminal on the left. Multi-build the central debris left and have one character jump on the pad enough times to reach the lever. Switch to another character, smash and rebuild right and jump on this new pad to access the other lever. Jump down the ladder.
In the next area, head all the way right up the stairs and then back left on the second level, deal with the two troopers and then smash the blue circle object. Multi-build right and jump on the pad as Han (Finn should automatically stand on the elevator). Jump up to the handle as Finn (this bit can be a bit buggy as the AI doesn't want to stay still - just keep at it) and switch to another character once he's hanging. Smash the multi-build and rebuild in the centre. Pull the handle out as Chewie, switch to Finn and jump to the next point. Switch back to Chewie and let go of the handles. Back to Finn, jump up, open the circular line with the lightsaber and destroy the troopers. Smash the silver locker right at the back of the pool area and multi-build left. Grab a Stormtrooper helmet from the machine. Head all the way back down and access the Stormtrooper terminal to unlock the red barrier. Head through and right for another Blaster Battle (and another opportunity to get all the Blaster Battle achievements should you still need any - see the Prologue for instructions). Shoot the target on the left side above the trooper behind the barrier, and then pull on the grapple that appears to deal with him. Switch to Chewie, shoot down the sentry droid and throw a thermal at the silvery parts of the gangway above you in the centre. Switch to Han and use the scan point on the right side. Scan the pipe above and ahead to reveal two grapples, which you'll need Han and Finn to pull together. Blaster Battle over, so deal with the rest of the Troopers as you wish before building the orange handles right at the back of the corridor. Pull on them as Chewie to reach the boss battle. Shoot the troopers until Phasma chucks a thermal at you (run away!), she should roll off to the left side. Once she's fired her cannon for a bit a door should open underneath her - throw a thermal at the metal panel to deal damage. Wait for her to head to the right and repeat the process. Once she's on the big rocket launcher in the middle, wait for her to fire her lasers and rockets twice and then pop one of the two targets. Rinse and repeat and then mash the prompted button to finish.
Here is a video walkthrough:
Credit to HappyThumbsGaming.