Do anyone know how to reset your login days?

What do you mean by "reset"?

If you have a streak but you're trying to set a new "Day 1," just don't log in to the app or site for a day. Fully log out and close the app on your phone, wait 30 hours, and log in again. Your streak will be reset to 0.

If you didn't or couldn't log in for a day, thus breaking your streak but now you want it back, go to https://www.myfitnesspal.com/account/login_counter_reset_request and enter the correct number of days.