It sounds like you initially started the containers without having a
config.env in place, or with the
MYSQL_PASSWORD variable empty.
You'll need to do the following:
then delete the
shared folder (this will delete any media items or database backups you have stored there, so back these up if they are important to you).
config.env exists, and that it contains a password for MySQL to use. Then run
docker-compose up -d or whatever the
up command you are using is from the install guide.