Can't reclaim infested world?

Noob here, in my first playthrough, base game only. Going well so far, have a nice federation going and just managed to fight back the invading swarm thing. At a high cost though, they invaded my core system and destroyed my home planet. Now it's an "infested world" and I can't colonize. I googled and it said to bombard, but I don't seem to have this option, maybe because I built a starbase and reclaimed the sector? Like, I can't bombard my own planets? Bombing policy is set to "selective" so I think it should allow it...