If you wish to play the game with a friend, follow the steps below to enter the HQ code of the Sentinel HQ your friend is in, or you can create a private Sentinel HQ and play with your friend there.
How to visit another Sentinel HQ1. Open the Options menu.
2. Go to the Community tab.
3. Enter the code for the Sentinel HQ you wish to go to in the "HQ Codes" option.
You can confirm the HQ code of the current Sentinel HQ you are in from the top right of the Community tab.