To enter a Docker container that is already running with a TTY, you can use the "docker exec" command with the "-it" flags. The "-i" flag allows you to interact with the container's STDIN, and the "-t" flag allocates a TTY for the container. Here are the steps to enter a running Docker container with a TTY:

List the running containers with the following command:

docker ps 

Copy the Container ID or Container Name of the running container that you want to enter.

Use the following command to enter the container with a TTY:
docker exec -it <container-id-or-name> /bin/bash

Replace <container-id-or-name> with the Container ID or Container Name that you copied in step 2.

Once you run the above command, you will be dropped into a new shell inside the running container with a TTY allocated. You can now execute any commands inside the container as you would normally do on a terminal.
When you are done working inside the container, type 'exit' to exit the shell and return to the host.