Since you already have it installed, you just need to to make sure you have the stop/remove commands in the defined script as such:
docker stop frndlytv-for-channels
docker rm frndlytv-for-channels
docker pull matthuisman/frndlytv-for-channels
docker run -d --restart unless-stopped --env "USERNAME=user@email.com" --env "PASSWORD=xxxxxxxx" --name frndlytv-for-channels -p 8183:80 matthuisman/frndlytv-for-channels
That will stop, remove, pull, setup the container, and restart it. [Only Include the Stop and Remove lines if you already have the docker container.]
Two additional variables that are not required but may be of interest are:
The --env "IP=xxx.xxx.xxx.xxx" is only if you want to change the geo-location that LocalNow uses. I do not believe it affects any other channels. It is by default the internet IP of your server.
The --env "KEEP_ALIVE=xxx" is mainly useful for people experiencing timeouts or problems with recordings not starting due to timeouts. Some systems can't login to Frndly fast enough before Channels times out. The keep alive will check every xxx minutes to make sure the token has not expired (thus no need to login). If it has expired it will re-login to get a fresh token. Every 5 hours it will re-login whether or not the token has expired. The default is 0 (off) as most users do not need keep alive because their systems connect fast enough for the regular "on-demand" tokens. (This is discussed about 100 posts up, lol).