Recovery

Reset sudo password
By default, the Steam Deck's 
deck user has no password set. In order to do some customization tasks that require system administrator access, a password needs to be set using the 
passwd command.
Follow the below steps to remove the password in case you forgot.
Acquire recovery media
Go to the Steam Deck Recovery Page and download a recovery image.
Flash the recovery image to a USB key according to the instruction on the Steam support page. If you don't have a USB-C key already, you will need a USB-C hub to connect regular USB devices to it (this will also allow you to connect mouse and keyboard for easier input).
Remove set password
In the recovery environment, open "Terminal with repair tools". This will open a terminal window.
To enter the local installation of SteamOS on your Deck's internal storage, 
chroot into it:
sudo ~/tools/repair_device.sh chroot
You are now hooked into your Deck's internal storage.
Proceed to remove the 
passwd and 
shadow overlay files, resetting them to their defaults:
rm -f /var/lib/overlays/etc/upper/passwd
rm -f /var/lib/overlays/etc/upper/shadow
The password on the 
deck user is now removed. You can now reboot your Steam Deck.
Set new password
After your Steam Deck has rebooted, enter Desktop Mode. You can set a new password by either:
Opening "System Settings", going to "Users" and setting a password for the only user available
Opening "Konsole" and executing 
passwd to enter a new password