Step one: Become a life planet by spawning as one, or from an asteroid as long as you have any star unlocked.
Step two: Get your mass (which can be seen on the top left) to one asteroid away from becoming a star.
Bonus step: Get an asteroid into your orbit.
Step three: Spawn as a star in the spawn menu, and find the life planet you just were playing as.
Step four: Bring your life planet into your orbit and get an asteroid into the planets' orbit (or skip this last part if you followed the bonus step).
Step five: Press space and you're done.
Note: This method stops working after you have a like 6 stars in one system (I forgot how exactly how many) and I hope this helps the like 5 people still playing this game.