If the locally running db you wish to connect to is itself running in a docker container then please run: docker inspect and find the Gateway IP address in the "networks" section. Use this IP address as the server address in Tonic.
If the locally running db is NOT running in a container but is just running on the machine then you can use the address: host.docker.internal if you are running on Windows or Mac. If on linux you can use 172.17.0.1 which will be the IP address of the docker0 interface.
Click on the Tonic logo in the upper left corner: