Add this to first request’s pre-request script:
pm.environment.set("resetValue",pm.collectionVariables.toJSON().values)
This wiil store all initial value to resetValue variable
And in the last request’s test script use
pm.environment.get("resetValue").forEach((a)=>pm.collectionVariables.set(a.key,a.value))
Now we are resetting all collectionVariables to the initially saved value