Select in field, include to selections not override
I have a requirement where I create multiple buttons each have a Select in Field action in them, assigning FieldName only 1 value. But, if a button has already been clicked meaning FieldName already has a value and user selects a different button, I want the new value to be included to the already existing.
First user click-
Current Selections: FieldName = FieldValue1
Second user click-
Current Selections: FieldName = FieldValue1, FieldValue2
If I simply put FieldValue1 or FieldValue2 on their respective button actions it overrides the existing selection and I don't want that. Is there a way to include the value to the selections?