Most instructions for running Pihole using Docker set the password as an environment variable in compose.yml. It’s in this section:
environment:
TZ: 'Europe/London'
FTLCONF_webserver_api_password: ''
FTLCONF_dns_listeningMode: all
You can set the password as a blank (as above) from the outset, then run
$ docker compose up -d
which will start the pihole container with no password set.
If you have one set already, you can change the password on a running container by determining the docker container id for Pihole (it’s the first field generated from docker ps -a, and then use the following command to set the new password (or delete the password altogether):
$ sudo docker exec -it "ContainerID" pihole setpassword
Enter New Password (Blank for no password):
[✓] Password Removed
$
If you delete the password altogether it will be reset to whatever is in the environment variable when the container is restarted, unless you also edit the compose.yml file.