Just remove the files you created during the installation in steps 1, 2a and 2b of the instructions and restart the container stack using
docker compose down and
docker compose up -d again.
/data/conf/portainer inside your mailcow folder.
The most important part is removing
docker-compose.override.yml (or the Portainer-specific configuration in this file if you are using additional overrides) so Portainer doesn’t run anymore.