Change Monitor Refresh Rate in Windows
You can press Win+I to open Windows Settings. Having done this, go to System > Display. On your right-hand side, you will find an option called Display adapter properties.
Click on it and switch to Monitor tab after opening the Properties window. In this window, you will see a drop-down menu where you can select other given refresh rates.
Select 30 Hertz and save your change.
If you have more than one monitor, you need to select the monitor before clicking on Display adapter properties button on the Display page.