Clearing variables at the end of a Datafile loop

I have a collection that uses a Data-file to loop through placing orders for approx. 60 new products (using a productId guid). To set-up this I have to first create two access_tokens, and a new transactionId, all of which are saved as collection variables.
I also have a “SetNextRequest” step which will bypass these three steps if the variables are populated, meaning they are only run once for each datafile run, rather than running for each new product.

if (pm.collectionVariables.get(“createdTransactionId”)) {
postman.setNextRequest(“Order01: Order submission”)

How can I clear these variables when the entire datafile has run, rather than clearing the variables when each new product is placed (which is what I have currently).

Ideally I would have a “clear variables” step at the beginning of the “loop”, but I only want it to run once at the very start of the run.

Any suggestions would be appreciated.