You can't. Apple's iPads and iPhones are e-waste from the moment they run out of security and OS updates. Apple doesn't allow third party installations.
It's technically possible, but there aren't any proper instructions, I assume it's pretty complicated and you could break the device while doing this. Also, I don't think it would run particularly well, since there are no Linux drivers for Apple's proprietary hardware (except for M1 because it was reverse-engineered, but iPads use A-Series chips)