See this article for information about updating payment methods on various platforms (iPhone, Mac, etc.): If you need to change or update your Apple Account payment method - Apple Support
Here is how you update your payment method on an iPhone or iPad:
1. Open the Settings app.
2. Tap your name.
3. Tap Payment & Shipping (formerly Media & Purchases). You might be asked to sign in with your Apple ID.
4. Tap Add Payment Method, enter the new payment method, then tap Done.
5. Tap Edit.
6. Tap the red delete button next to the old payment method, then tap Delete.
Also note:
1) ”If you change your address, the credit or debit card information that you use with your Apple Account might be automatically updated by your financial institution, and you don't need to take action.”
2) “If there's an issue [such as you having a subscription or being a Family Sharing Organizer], add a new card first, then remove the old card."
If an app or feature on your device is not working, not appearing, or is restricted (grayed out), it may have been disabled using Screen Time, or by an IT administrator if you are using a device owned by an employer or educational institution.
- Read this support article If your Apple ID or other options are greyed out in Settings —> If your Apple Account is grayed out in Settings - Apple Support
Tap Settings > Screen Time > Content & Privacy > scroll to Allow Changes and turn on.
- If the device is managed (Settings > General > VPN & Device Management), contact the IT department that is doing the managing.
The above is the standard procedures for updating payment methods, but as noted in an earlier reply, it requires account access. Given your situation you may wish to start investigating a long-term solution to your spouse's account. Apple unfortunately doesn't really have a solution for accounts where adults have diminished capacities, so hopefully you can still resolve this at this point. If not, give Apple a call and see if they have a solution. The only one that I know of is is a person is deceased which is clearly not the situation here.
This support article has various country telephone numbers for contacting Apple for support and service ➔ Contact Apple for support and service - Apple Support For some countries look under “Other” listing at the end of each region. Not every country has telephone support.
Good luck!