The device password set during installation protects the BitBox02 from unauthorized access. This means, if you forgot your device password, you no longer have access to your BitBox02. However, the device password just protects your device and is not part of your backup, which is why you don't need it for recovering your wallet.
You probably already noticed the warning on the display of your BitBox02, informing you about how many tries remain for entering the device password. To ensure no one can easily break into your device by trying a bunch of different device passwords, the BitBox02 will automatically reset to factory settings after 10 wrong device passwords have been entered. This security mechanism is what we will now use, to intentionally reset the device.
Ensure you have your backup ready, i.e. your microSD card or the recovery words, to restore your wallet after the device reset. Now, repeatedly enter wrong device passwords until the device resets. Your BitBox02 is now in the same state it was when you first unboxed it. You will have to confirm a new pairing code in the BitBoxApp and on the device. In the BitBoxApp, you can now choose how you want to set up the device. Since you want to recover your existing wallet, select whether you want to use the microSD card or enter the recovery words manually on the right side of the setup menu.
Once you're done confirming the details or entering the recovery words, you can set a new device password. Even if you forget this new device password as well, you can always reset the device and recover your wallet in the future.
For a hands-on guide, watch our video on this question here:
Note: Do not confuse the device password with an optional passphrase. The latter is an additional security feature which, contrary to the device password, is part of your wallet backup and must be remembered if you want to restore access to your wallet. See our blog post for more details about this feature and its potential risks.