i was thinking of baking the tape, but nooo idea how to do that. never done it
As far as baking goes, does the tape leave a residue on the heads when being played? If not, then there's no point to bake the tape IMO as this is typically done to avoid sticky shedding of the tape during playback, which gunks up the heads and wrecks the tape itself after a while. And that is typically an issue with (open) reel tapes of the '70ies.....I haven't really heard of anyone baking a cassette tape, but it could be done I guess.
Aside from that, I have to agree with others in this thread: If that tape is really precious and uncirculated it should get a proper transfer with azimuth adjustment, without it you'll never achieve a satisfying result.