The reset date of your account follows your billing cycle. For example, if you are paying on the 8th of the month, your account will reset on the 8th automatically.
By reset, it means
your monthly posts count will reset
What remains the same:
Number of trackers given
All of your data collected will stay in your account as long as they are not deleted
You can also find the day your account will reset directly from your Keyhole account, just go to Settings > Billing / Subscriptions > View Invoice: