WARNING: between 10 September 21 and 5 December 21, nobody managed to unlock this achievement (except people set to non-stat tracking). Several people attempted it and failed. It appears to have been fixed by the 4 December update, and the instructions below are working again. If you have issues, post in the comments.
TL,DR: seems to be fixed - working since 5 December 2021
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Load the game, and select the 'Moon' level in free play.
Make sure you're in 'build mode' rather than 'drive mode' (press
if needed), then press
left on the D-Pad 
to switch into alternate building mode, which means items can be placed in mid-air.
Press
to open the spawn menu, and find a bicycle-with-basket under 'vehicles'.
Press up on the D-Pad
to rise up (best to do this a few times), and place the bicycle in mid-air.
Press
again, and find an alien passenger under 'sci-fi' (bottom row) on the far right. Hover directly over the basket, and place the passenger in the basket.
EDIT: If it doesn't pop, AlbinoKidELITE suggests placing the bike high up in the air, and YodaFreak1984 suggests making the alien face the same way as the bike. You can rotate pieces with 
.