You cannot change canvas control values (selects, checkboxes etc) with an action.
Instead, make a table or a few tables that would serve as controls. You can modify values in the tables with ModifyRows(), and you can use them in formulas with some extra work.
Here’s some inspiration:
This is a table:
I have an SwitchIf() formula that populates a different list of values for different rows. Then I refer to these rows in filters by row reference @Select company.Value
And this is a table, in Detail view to simulate a form:
When I use the stopwatch to track time, the “Log to current task” button adds tracked time to what’s selected in that form.
And here’s the table that shows all tasks for selected client, and each task has a button to modify the “Current task” value to set thisRow as a current task:
