Got a new Switch, old one broke two years ago, I have inherited very old Switch save data which I don’t want, Online help says office is in Covid lockdown so they can’t help me, which is clearly very old text. Sooo, what do I do? I do NOT want to make a separate Switch profile just for this game.
I don’t know if in switch is the same but in the steam version is in settings then account, should be a delete account option.
There is no such option in the Switch version. I wouldn’t have needed to post this question if there was. 
You might try here, if Switch hasn’t received in-game account delete option yet.
https://gemsofwar.zendesk.com/hc/en-us/requests/new?ticket_form_id=360000013555