It looks like that was chapter 33, Trisolaris: Sophon
If you want to jump in and read that chapter, all you need to know is this:
!the aliens are on a planet in the alpha centuri/proxima centuri trinary star system, the closest stars to the sun. Also, apparently the three suns means it sucks there and they’re desperately looking for a new star system.!<
It looks like that was chapter 33, Trisolaris: Sophon
If you want to jump in and read that chapter, all you need to know is this: