The counter should reset after 24 hours since last e-mail. If it doesn't do so, please follow the steps below:
Please backup your entire website. Export your database as well.
Please terminate your current website: 000webhost cPanel > Settings > General > Delete website
Create another website and restore the backups.
This should fix the problem. We know there are some issues with the counter and a fix for it is on our "To-do list" already. We are sorry for inconvenience.