How can I change the current annual bill amount?

I have a payment issue with the software Mirror. I need to make a payment on April 30th this year, which is $576 annually for this turn. However, there was an error in my previous payment setup. When I noticed this, I wanted to adjust the number of members to reduce the payment amount. But after I modified the number of members, the annual price for April remains $576. I hope to adjust it to the annual billing price for a single user than pay it. What should I do? Otherwise, I will have to pay 5 times more than necessary.