Hitting with fist can increase base damage, as in a combo (1.21.6)

I am trying to make a combo system where a player with a certain tag (tag1) hits with their fist, their base attack_damage attribute will increase by 2. This would reset if the player had not made a hit (with their fist) within the last second.
I'm guessing that the hit detection would probably be done through an advancement trigger, but im unsure of how to adjust attributes more dynamically other than just setting their base manually.