I want to stop creating row when condition is true

in this blocks i want if its “true” to stop creating the row
because it’s now fires the notifier and creates the row and put “repeat” in the 'national ’ field and if it was “false” it creates the row with the value from textbox without any problems

Perhaps the solution would be first to insert the values of “national test” in a variable. Afert make a list

global id is a list?
what about using a default if statement in the button click event like this

if is in list? ...
then diplay the notifier
else Spreadsheet.CreateRow...