To detach from a screen (i.e. you want to close the SSH connection while mining continues afterwards) it's
CTRL + a + d
To reattach to a screen (resume connection) it's
screen -x [name you gave the screen session] # once you've typed 3-4 characters hit the tab key and it will fill out the rest and save you some typing
If you can't remember what you named the session use:
screen -ls
If you're new to screen you may not know you can open a 2nd shell and switch back and forth (i.e. your miner is running on one shell and you open a 2nd to run nvidia-smi):
once in screen you create a 2nd shell (or 3rd, 4th, etc) with
CTRL + a + c
To switch back and forth use:
CTRL + a + n