Sugargoo, like many other agents, requires you to purchase a certain item that will extend the storage period. It costs 20 yuan. Here's the link to the storage period extension: https://sugargoo.com/index/item/index.html?tp=mall&tid=328&partnercode=UmVwQXJjaGl2ZQ==
In the remarks you have to leave a comment, explaining which item to apply it to.
In my case it gave me 8 extra months of storage, but that might be due to a Covid incentive they had, I'd assume it's 6 months regularly.
added: 6/26/2023
Other ways to ask
How can I get more time to ship my items on Sugargoo?