Whenever you set the variable inside the scenario itself, it will start with the hardcoded value every time.
If you want it to be persistent between executions, you need to store it permanently somewhere else.
You can use make’s own Data Store, creating a data structure that only holds a number. Or you can use anything else that can hold a value, like a Google spreadsheet.
Just remember to read the value, increase it by 1 and update it on every run.