Much like pre-ordering a book before it is published, you can place the new order on CMP up to 5 days before the renewal date of the existing subscription (that was ordered through the licensing desk / PPA). If the order expired less than 60 days ago you can also reactivate via CMP. If the old subscription expired more than 60 days ago then the account information is likely deleted and a new order will need to be placed.

See this article for how to place the order: How to purchase IBM MaaS360 from Cloud Marketplace