The option to sort collections currently doesn’t exist within Postman. So I have created this collection that will sort any collection alphabetically. You will need to supply the collection ID and workspace ID along with a Postman API Key.
It will pull in the collection JSON, sort it alphabetically, create a new collection with the sorted HTTP requests and then delete the original (unsorted) collection.
Instructions can be found in the collection documentation.
Fork the collection here: Collection Alphabetiser