@girish Worked like a charm. Thanks Girish!
To make it easier for other noobs like myself, do the following:
Run these commands using the app's terminal in your Cloudron dashboard (one line at a time).
cd /app/data/db
sqlite3 wallos.db
UPDATE user SET username='your_new_username' WHERE username='admin';
CTRL+D
Notes: Replace your_new_username above with your chosen username. Restart the app. Now, log in using the new username and your old admin password.
P.S. Use Ctrl + Shift + V for pasting in the terminal.