How can I change payment due date for a subscription

It seems you're talking about the day a subscription renews. You would have to cancel the subscription, wait for it to end (expire), then start it again on the desired date. Note that for some subscriptions this may entail loss of data (such as playlists for Apple Music) or other features.

View, change, or cancel your subscriptions - Click on the link to learn "How to cancel a subscription from Apple." --> If you want to cancel a subscription from Apple - Apple Support

Check if this helps -> How to switch to a different subscription plan

How to switch to a different subscription plan - Apple Support