Hello, and welcome!
If X.Org automatic configuration is not working for you, you will need to configure
/etc/X11/xorg.conf manually.
This link shows an example file with two forced resolutions: 1024x768 and 800x600.
You will need to review your
/var/log/Xorg.0.log file to determine which video card and monitor are discovered and used.
You will need to adjust the
HorizSync and
VertRefresh values to match your monitor's technical specifications.