Do you mean …
On the 1st of the month reset all the counts … ?
Or … Reset the Counts 1 month after the User has signed up.
The former is much simpler, and I would suggest just having an admin button on a password protected page (or you could even run an API workflow from the Data Panel). So just do it manually on or around the 1st of the month.
The latter is tricker but not that hard, when the user signs up, you run an action in the workflow that schedules an API workflow for 1 months time. Passing in the User.
In that API workflow you would then just reset the User’s count.