How do I change billing on ICloud

I am not clear on what exactly you mean by "change billing on iCloud+"

If you meant how to change your iCloud+ plan then follow the instructions in this guide 👉  Downgrade or cancel your iCloud+ plan

If you mean how to change the payment method for your Apple ID (iCloud) then follow the instructions in this guide 👉 If you need to change or update your Apple ID payment method.

If you meant something completely different than what I have understood then please provide detailed information related to the issue that you would like to be addressed.

Axel F.