Is it expired?  If it’s still active, have your seller complete a ‘Exclusive Right to Sell Modification to Contract’ form with a new expiration date. Then, simply go into the MLS and extend the listing [listing edit screen, go to status and extend or expire]. The MLS Office doesn’t need any paperwork (unless there is a dispute later).

If the listing is expired, you have 31 day in which to obtain a ‘Exclusive Right to Sell Modification to Contract’ or written instruction signed by all parties to extend the listing.  Then, you can do a full copy (in the menu) and simply enter the new expiration date. The days on market continue to accumulate just as an extension. You will upload the modification when entering.

If the listing is expired, and has been off the market for more than 31 days, you will need a new Exclusive Right to Sell agreement signed and then it’s entered as a new listing. You may, however copy an old MLS listing of your own and update the fields and photos where appropriate.