Reset the data count on a firewall rule

This is not possible. Counters are currently from reboot to reboot. There is a feature request for this I suggest you upvote:

https://ideas.sophos.com/forums/330219-xg-firewall/suggestions/34656040-zero-firewall-rule-traffic-counter

Having said that, you can see counters for each rule in a more targeted fashion by going to Reports and using the pulldown menus to choose "Traffic Dashboard" and "Allowed Policies" and then choosing the date. This would give you traffic for a more specific time period. You do not have the option to choose a time, which would also be wonderful, but can choose by days.

This is not possible. Counters are currently from reboot to reboot. There is a feature request for this I suggest you upvote:

https://ideas.sophos.com/forums/330219-xg-firewall/suggestions/34656040-zero-firewall-rule-traffic-counter

Having said that, you can see counters for each rule in a more targeted fashion by going to Reports and using the pulldown menus to choose "Traffic Dashboard" and "Allowed Policies" and then choosing the date. This would give you traffic for a more specific time period. You do not have the option to choose a time, which would also be wonderful, but can choose by days.