How to change the refresh rate of lightdm?

today i installed manjaro on the samsung flash f30 laptop. but there is a problem with the screen refresh rate. if the refresh rate is 59.9hz, the display works normally, but if it is 60.0hz, the display starts to flick and has overscan. this 59.9hz refresh rate was only applied in the xfce session, but in lightdm the refresh rate is still 60.0hz, so the display starts to flick and has overscan; so how can i adjust this refresh rate to prevent the screen from flickering?