From the Ubuntu manuals page for xvidtune – video mode tuner for Xorg:

Xvidtune is a client interface to the X server video mode extension (XFree86-VidModeExtension).

When given one of the non-toolkit options, xvidtune provides a command line interface to either print or switch the video mode.

Without any options (or with only toolkit options) it presents the user with various buttons and sliders that can be used to interactively adjust existing video modes. It will also print the settings in a format suitable for inclusion in an xorg.conf file.

Normally the Xorg X servers only allow changes to be made with the XFree86-VidModeExtension from clients connected via a local connection type.

Note: The original mode settings can be restored by pressing the ‘R’ key, and this can be used to restore a stable screen in situations where the screen becomes unreadable.

Emphasis added. We had not heard of Xvidtune before, and it seems like it could be a handy tool to have in certain situations. See the manual page for your Linux distribution, or the Ubuntu manuals page for xvidtune for additional information. However, Tecmint warns:

Note: The Incorrect use of this program can do permanent damage to your monitor and/or Video card. If you don’t know what you are doing, don’t change anything and exit immediately.

Source: 8 Useful X-window (Gui Based) Linux Commands – Part I (Tecmint)