Creat an app backup first.

If you are in the web terminal of your Invidious app, look to the top right corner.
There is a big green button labeled Postgres.
You can just click that button and confirm with ENTER. Then you are logged into your Invidious PostgreSQL database.

From the official documentation you still need to do:

python3 -c 'import bcrypt; print(bcrypt.hashpw(b"<INSERT PASSWORD HERE>", bcrypt.gensalt(rounds=10)).decode("ascii"))' # python
mkpasswd --method=bcrypt-a -R 10 # mkpasswd

Now you have your new password hash.
Connect to your PostgreSQL database with the described button or copy and paste the following into your web-terminal (the button will print the same into your web terminal):

PGPASSWORD=${CLOUDRON_POSTGRESQL_PASSWORD} psql -h ${CLOUDRON_POSTGRESQL_HOST} -p ${CLOUDRON_POSTGRESQL_PORT} -U ${CLOUDRON_POSTGRESQL_USERNAME} -d ${CLOUDRON_POSTGRESQL_DATABASE}

Now you should be able to update the password:

UPDATE users SET password = 'HASH' WHERE email = 'USERNAME';

I will request an update of the Cloudron documentation for Invidious to include the password reset with the Cloudron way to do it.
Thanks for reporting this missing documentation and please report back if everything worked out on your part.

~Cheers