Hi. I fixed it in the end. I can't remember the exact commands, but this might help someone.
I stopped mysql
sudo /opt/bitnami/ctlscript.sh stop mysql
I ran a command like:
/opt/bitnami/mysql/bin/mysqld --skip-grant-tables --skip-networking --user=root &
then it allowed me to do something like
mysql -u root
that got me into mysql. Then I used one of the two syntax from here
like UPDATE mysql.user SET Password=PASSWORD('NEW_PASSWORD') WHERE User='root';
but I think I had to use 'use mysql' or 'use users'
'quit' at the end
then i restarted mysql.
Sorry that's vague but it did work so stick with it.