Cancel the expired subscription

If the subscription is expired, you can't cancel it.

Purchases - View, change, or cancel your subscriptions.        

Purchases - Subscriptions not billed through Apple  

Link to contact Apple Support at the end of the article.

Purchases - the subscription that you want to cancel is not listed   

See the Apple Support article(s) below. Link to contact Apple Support in the article.

Apple ID - If you see ‘itunes.com/bill‘ or an unfamiliar charge on your bank, credit card, or debit statement.

(If the subscription is expired, you can't cancel it.) than how do I fix it? Do I have to buy subscription and cancel it?

If it is expired, you shouldn't have to do anything. Why do you think you need to do something? Are you still being charged for the subscription?