You need to go through the actual organizer's account, you can't do anything from your account.
You need to log in to the organizer's account on an Apple device, or Windows Pc or through the https://account.apple.com website and change the payment method there.
You can also change the email address associated with it if required.
There is no further ownership to change beyond that.
If you can't access the account, then you will need to leave the current Family Sharing group and start a new one.
click here ➜ If you need to change or update your Apple Account payment method - Apple Support
and here ➜ Change your Apple Account primary email address - Apple Support
If you don't have the password for the Apple Account, the you may be able to request access.
click here ➜ How to request access to a deceased family member’s Apple Account - Apple Support