There's no way to start over from scratch unless you make a new account, or just buy new players. I have so many items from a previous game from a year ago and I don't remember what was good or bad, so I'd rather just start over. This is a fairly simple feature in most games, and I think it should be added to Card Hunter.
I think you can write to support@cardhunter.com if you really want to start over from scratch. Just mention you would like your account to be reset and remember to specify your in-game username in the email.
For standard single player RPGs, yeah. For most CCGs or most online games, it's incredibly rare to have an account reset that doesn't have to be done manually by the devs. Especially in a game where you can [Steam's logout issues aside] make a new account so very easily. I'm not sure why you'd want to unset items, since you'll have to figure them out as you get them again anyway [which isn't to say I don't respect your right to that perspective], but perhaps if you clarified why it's an issue for you, it could be addressed a bit easier. For example, is it item organization that makes it stressful to rejoin your active account? Is it a desire to run through the game dialogue and tutorial again? If it's a specific element, perhaps the devs can address that, instead.