Here is a description from the walkthrough writers of how to complete the level as well as earn some other achievements along the way:
At the start of the mission you can switch to R3-Z3 and scoot into the icy cloud on the left for Minikit 1. You can also run right into the foreground as any character and drop off the ledge to get Minikit 2 next to some traffic cones. Continue right and defeat the Snowtroopers, then head through the toxic cloud and destroy the glowing object. Multi-build left first to allow your third character through, then multi-build right to build a boost pad. As C'ai Threnalli, blow up the silver object in the ice at the back and then use the boost pad to jump over. You'll need to destroy the targets on the crashed X-Wing above and then push the crate down. Build up a grapple hook and then switch to Lieutenant Wright to pull it. Build a bridge and walk across (mashing the button when prompted to keep your footing). Get up to the right of the crashed X-Wing and pull down the tree in the background to get a multi-build. Build right first to turn a piece of the track the right way round. Then build left to make a switch, and bounce on it to charge up the battery. This will send a claw thing around the to big metal door. Press the button when prompted to smash down the door.
On the other side, defeat the hot tub Troopers and switch to C'ai to climb the stud wall behind them, netting Minikit 5. Head right and you'll enter a Blaster Battle.
First thing you should do is shoot the bullseye targets in the upper left and upper right of the battle to get:
Defeat the regular troopers and then you'll get a scan point on the right-hand barrier. As C'ai, focus on the bottom of the sniper tower. Throw a Thermal at the silver section and then switch to Wright to pull on the grapple. Defeat all of the Troopers in the next section (there's one way up at the back of the screen, partially obscured by the crashed TIE). After everyone's down, you'll get a cutscene and then you'll be able to blast the side of the TIE fighter to deal with the shielded Trooper. After the battle, head to the back as Wright and pull on the grapple to bring down an X-Wing. Build the debris into a switch that R3-Z3 can use. Head up the ramp to the left and get in the vehicle.
On my first playthrough, the Snowspeeder controls messed up. Unless I was holding down cn_RB, I was unable to move the speeder, I could only move the aim. On a second playthrough the controls seemed to sort themselves out.
You'll need to stay sharp to get Minikits 8, 9 and 10. You need to shoot down three TIE fighters in the first section to get Minikit 8, which is difficult because the scene is so chaotic. It's hard to even describe where they are. There are four or five in the first half of the vehicle section, and they are all dogfighting in the top third of the screen, so keep your sights trained up there and do what you can. There's one easy TIE to get on the final jump of the section, where time slows down briefly. However, for Minikit 9, on this same jump you need to veer to the right of the screen to grab it, making it difficult to go for the TIE fighter and the Minikit at once. Do your best, but be prepared to do this section again (there's a checkpoint at the beginning of the vehicle section).
After the first part of the on-rails vehicle section, you'll get:
During the second half, keep shooting at the top-left of the screen, at the icicles on the left side. One of them contains Minikit 10. After the second part of the chase, you'll finish the level.
Here is a video walkthrough:
Credit to HappyThumbsGaming.