How to fix black screen on a reTerminal after connecting to an external monitor?

How do I fix a black screen after connecting the reTerminal to an external monitor? Do I have to reinstall the operating system and never connect to an external monitor again? Is it not possible to use the reTerminal screen and periodically connect the reTerminal to a monitor?
I recently acquired 2 reTerminals. On the initial setup screens of the reTerminal it had the option to connect to a monitor, so I checked that option. I followed all the setup and software updates and everything worked fine. After that I connected it to an external monitor using a microHDMI cable, and it works fine on the monitor, but now my reTerminal only has a black screen. It only works connected to an external monitor now. Reeboot and power off/on did not make it go back to showing anything on the reTerminal screen. I did not make any changes to the operating system. This happened to both the reTerminals I own.
Thank you for your help!

Hello, thanks fory your feedback, after reading your error we have test it, now you can follow the list below to reset it:

  1. connect your device with the external monitor, and use the vnc or the touchscreen to do the next
  2. open the preferences and enter the screen cofiguration
  3. make sure your DSI-1 device is Active
    here is the screenshot:

Thanks for your help!
The screen config was not working until I reinstalled the drivers twice. After the first time I reinstalled the drivers and rebooted I still had a black screen. After the second time and reboot, then the monitor and the screen config started working. After that I was able to flow the steps you suggested. Now I can connect and disconnect to an external monitor when I need.