First does allow you to reset your account if you are having an unpleasant experience with the data you have uploaded to your account. Resetting your account will erase all contacts from your account and allow you to start from scratch. We only allow account resets in extenuating circumstances.
We will always recommend First deleting a specific source from your account one by one to see if you experience gets better by just removing a small amount of contacts.
If you wish to reset your account, please contact product support HERE.