I cannot be specific (as you have not provided any information, only stated the issue) so you will have to dig around a bit.
Look for the Xorg configuration file used by your monitor (probably more than one) under '/usr/share/X11/'.
find /usr/share/X11 -name "*conf*"
The add\change 'true\false' in the following lines as required
Option "InvertX" "false"
Option "InvertY" "true"
Don't forget to duplicate the same changes to the mating file in /usr/share/X11/xorg.portrait.d/