How do I update Apple Card information after changing last name?

See the following excerpt from Update your Apple Card account information - Apple Support

Update your personal information

• If your name or phone number changes, call or chat with an Apple Card Specialist at Goldman Sachs to update your account information.
• If you no longer use the email address that's associated with your Apple Account, you can also update your email address.
• If you want to update your legal name or select a chosen first name to be displayed on your Apple Card, call or chat with an Apple Card Specialist at Goldman Sachs. Once updated, you can request a new Titanium Card in the Wallet app.

You should notify an Apple Card Specialist for a name change.

CONTACTING — Goldman Sachs Bank 

• Using Messages; chat with an Apple Card specialist

• Call toll-free at 877-255-5923

• Write to: Goldman Sachs Bank, Lockbox 6112, P.O. Box 7247, Philadelphia, PA 19170-6112.

He’s a few other places to update.

Update your Apple Card account information - Apple Support

Change personal information on an iPhone 

1. Open the Settings app
2. Tap your name at the top of the screen
3. Tap Personal Information
4. Tap your current name
5. Enter your new name
6. Tap Done in the upper right corner

You should also contact an Apple Cash Specialist and change your name.

Contact an Apple Cash Specialist at Green Dot Bank by calling (877)-233-8552