How do you realize losses from a bankrupt company?

Hello all, I could not really find any good info for this by googling so thought I would come here instead. I sold PLTR almost 2 months ago for a capital gain, and to avoid taxes I would like to claim losses on a bankrupt company (Fisker, I just believed in them too much and let my heart do the talking) that is just sitting in my Schwab account. Cant sell the worthless shares, but is there anyway to make these unrealized losses become realized? Or is it just a wait it out game?