You can do this easily with a simple function block, specifically Integer Scheduler (T19), or Bool Scheduler (T17). Signal from these can be used to trigger a function block which sums the value from a counter to some stored value, and the nulls the counter afterwards.
I recommend looking through some online tutorials on function block diagrams (FBDs) and structured text (ST), as well as thoroughly reading the "help" topics in the IDE (press F1).