Any non-prescription help for someone with ototoxicity from past medications?

No. Ototoxicity may be temporary as occurs from an overdose of Aspirin improving by just stopping the aspirin, or it may be persistent or even permanent as from toxic doses of streptomycin, gentamicin, or furosemide. I'm not aware of any medication you can take, prescription or over the counter, that will help. Avoiding further exposure especially at toxic doses is the key.