See which port pgadmin is running on, if already running. Usually it is port: 8081
docker exec < containerNAME > env : shows env variables for a container - this is required for installation below.
docker stop <container_id> if there is already a docker running pgadmin
docker run -p 8081:80 -e 'PGADMIN_DEFAULT_EMAIL=user@domain.com' -e 'PGADMIN_DEFAULT_PASSWORD=SuperSecret' -d dpage/pgadmin4 - this command assumes 8081 port and also obvoiusly replace your email and password.