Remove the old freebie. Bring your obj into a modeler, or uv mapper, whatever...

Flip the uv map, not the texture.

Upload the new version

It's perfectly acceptable, would take less than a half hour of your time. As Bagginsbill used to say 'stop faffing about'

Not being rude or insulting but this is elementary modeling stuff, it's a freebie, and you're making this waaaay more complicated than it needs to be and stressing unduly.

Best wishes.

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