After the opening, fight the attackers and then as Han Solo, head to the scan point. look at the large grey box on the right with your binoculars to find a shiny metal section. Characters such as Chewbacca can chuck a thermal detonator at these objects, so do that now. Time for a Blaster Battle. If you haven't yet popped the following achievement, there's another chance to try if you make sure you are playing as Han (see the Prologue above for details on how this achievement pops)
Regardless, just keep popping enemies on either side of the turret until you are automatically switched to Finn and Rey. As Finn, head left into the green smoke and turn the wheel to switch it off. As Rey, jump right using the boost pads in the foreground and use your staff to get across the swing bars. Smash the box immediately left to build a staff point, which you can turn to lower the bridge for Finn. Finn should head up and pull on the grapple point, and then shoot the target behind it.
You'll switch to Han and Chewie. All you need to do here is throw two thermal detonators at the two locks barring the red tentacled rathtar squirming under the floor. No need to shoot anyone, the Rathtar will deal with it. Head right.
Red Brick - DEFINITELY get this one, as it's Studs x2, very useful. All you need to do is pull the grapple point to the left of the door as Han. Grab it!
As BB-8, head through the small grate right of the door. Jump on the BB-8 pad. All you need to do here is get the ball through a series of gates by pressing the buttons attached by wire to each gate. It's very simple, although a bit buggy - if the ball is completely immobile despite not being near a gate, quit out of the mini game and head back in.
Back to Rey and Finn. Head all the way right until you see a shiny blue object by the dead end. Smash it and pick up the tube. Take it back left to the indicated point and shove it in place. After the chaos, just keep running until Finn gets tentacled. Smash the glowing boxes and multi-build right to pin one tentacle. As Chewie, pull the bars in the back right corner. Build a red object on the floor, smash the previous multi-build and rebuild forwards. Two tentacles down, now you can multi-build left and interact with the object to sever the final tentacle. Set both Han and Finn pulling on the grapple points on the door to the right to continue.
Final section. Kill all the enemies and the Rathtar will pick up a crate with a target on it. Shoot it and it will explode. Debris will appear to the left - multi-build forwards to reveal a climbing wall. Head up as Rey and use the staff point to turn and reveal a BB-8 point. Head back down, smash the multi-build and rebuild left. Use the BB-8 jump point to send the robot up to the top level, and access the lock puzzle.
Back in the centre, kill the new enemies until the Rathtar again picks up an explosive crate, which you should shoot. Rebuild the smashed pieces in the foreground, and then head right to the scan point as Han. Scan the top crate to the right. Throw one of Chewie's thermals at the shiny metal. Head through the green smoke as Finn and pull on the grapple point above and to the right. Multi-build to the left (red pipes), smash and rebuild right (green pipes) and then middle (yellow pipes). Break the box and build a Crab Droid. Send that out to interact with the Rathtar. When it breaks, rebuild into a BB-8 pad. Get on it, wait for Chewie to get on the lift, send him up. Switch to Chewie and pull the bars. One last round of enemies, then shoot the explosive crate and build a cannon in the foreground. Blast the Rathtar until he's down. Head to the Falcon.
Here is a walkthrough video:
Credit to HappyThumbsGaming.