Q: Update AirPort Utility/Time Capsule with current iTunes password

Hello jslinsd,

I understand that you are seeing an alert that the Apple Id is incorrect. Let's see if we can get that sorted out for you.

It sounds like you need to update the Back to my Mac feature for your Time Capsule. Take a look at the quoted section below to walk you through updating the password. 

Set up and use Back to My Mac
https://support.apple.com/en-us/HT204618
 

Set up Back to My Mac

To get started, you need to set up Back to My Mac on each Mac that you want to use: 

1. Choose System Preferences from the Apple () menu, and click iCloud.
2. If you aren't already signed in to iCloud, enter the Apple ID you use with iCloud and click Sign In.
3. Select Back to My Mac.
4. Follow any setup instructions that you see next to Back to My Mac.
5. Set up security options.

If you want to access files on a hard drive connected to an AirPort Extreme or AirPort Time Capsule, follow these steps to set up Back to My Mac on your base station:

1. Make sure you're on the same local area network (LAN) as the AirPort base station that you want to set up.
2. From the menu bar, choose Go > Utilities and double-click AirPort Utility.
3. Select the AirPort base station that you want to use with Back to My Mac, and click Edit. If you don't see the base station, click Other Wi-Fi Devices to see a list of available base stations. You might need to choose a different Network Interface from the pop-up menu.
4. Enter the base station password. This password is different from your iCloud password.
5. Select the Base Station tab.
6. In the Back to my Mac section, click the + button and enter the Apple ID and password you use with Back to My Mac. You should see a green status indicator showing that Back to My Mac is turned on.
7. Click Update to save your changes.

Take care