Change password to Time Machine backup

Hi Carsten,

If you've forgotten your Time Machine backup, you may need to erase your disk that you use with Time Machine and then set up an encrypted Time Machine backup again.

If needed, the steps below show how to erase a disk in Disk Utility:

1. "If you have any files you want to save, copy them to another storage device.
2. Open the Disk Utility app  on your Mac using one of the following methods, depending on the type of disk or volume you want to erase:

• If you want to erase your startup disk: Start up your computer in macOS Recovery, then choose Disk Utility in the Recovery app. To learn how to start up your computer in macOS Recovery, see Intro to macOS Recovery.
  • Note: If you want to get your Mac ready to trade in, sell, or give away, and your computer is a Mac with Apple silicon or an Intel-based Mac with an Apple T2 Security Chip, use Erase Assistant.
  • If you want to erase any other type of storage device: Double-click Disk Utility in the /Applications/Utilities folder.

1. Choose View > Show All Devices.
2. In the sidebar, select the storage device you want to erase, then click the Erase button .
3. Click the Scheme pop-up menu, then choose GUID Partition Map.
4. If the Scheme pop-up menu isn’t available, make sure you selected the storage device you want to erase—it’s at the top of the hierarchy.
5. Click the Format pop-up menu, then choose a file system format.
6. Enter a name.
7. (Optional) If available, click Security Options, use the slider to choose how many times to write over the erased data, then click OK.
8. Secure erase options are available only for some types of storage devices. If the Security Options button is not available, Disk Utility cannot perform a secure erase on the storage device.
9. Click Erase, then click Done."

That information can be found here: Erase and reformat a storage device in Disk Utility on Mac - Apple Support

After that, you can then encrypt it by following this article: Choose a backup disk and set encryption options on Mac - Apple Support

We hope that helps.

Take care!