How to delete expired subscription ?

You cannot "delete" expired subscriptions on an iPhone, but you can hide them or wait for them to automatically disappear after a year.

To hide them, go to the App Store > Tap your profile icon > Tap Purchased > My Purchases, then swipe left on the subscription and tap Hide. 

What to Expect

• No Manual Deletion: Apple keeps a record of past purchases, so there's no immediate "delete" option for expired subscriptions.
• Automatic Removal: Inactive subscriptions will automatically disappear from your list about 365 days after their expiration.
• Hide for a Cleaner List: Hiding subscriptions is a way to remove them from your visible purchase history without deleting the record entirely. 

You can't delete subscriptions from your purchase history but you can hide them. See this document: Hide purchases from the App Store; click here --> Hide purchases from the App Store - Apple Support .

I have never seen Apple say anything about a 1 year time limit. If that is the case then it would be good to see a link to where Apple says that.

same I was wondering the same question.