How To Change Time Machine Password - Mac OS Extended (Journaled, Encrypted)
Remove and Re-Enable the Backup Drive from Time Machine With New Password

Open System Preferences &gt; Time Machine

Remove current disk: Select Disk... &gt; Under Backup Disks, choose the existing drive &gt; Remove Disk




Re-enable disk without the existing password: Select Backup Disk... &gt; Select disk &gt; Deselect Encrypt backups &gt; Use Disk



Cancel the disk backup in-progress &gt; Wait for the disk to decrypt

Repeat Step 2.

Re-enable disk with a new password: Select Backup Disk... &gt; Select disk &gt; Select Encrypt backups &gt; Use Disk