DeletedUser433 I see. Unfortunately I am not able to help you ensure data cannot be recovered on a hardware level.
Software-wise I would use Extirpater, which can be downloaded from F-Droid repo. Then I would factory reset the phone. As far as I know, factory reset should be enough to make data recovery impossible as the encryption keys are wiped.
Seeing you have already disassembled the phone it's probably not a solution for you.
You could also pay Nitrokey for physical destruction of the storage, if I am not mistaken.