You can export the config file (miner.json) from the settings page of your miner. In that file you can change the value of the frequency (MHz).
To edit the file, i use a tool called "Visual Studio Code" You don't need this tool cuz you can edit the file with the Windows Editor.
After you edited the file, you can upload it back to the miner over the Settings page -> miner reboots.

Change the value of auto_frequent from 0 to 1: "auto_frequent":"1"
Change the value of frequency from 900 to 950 or 1000: "frequency":"900" or "frequency":"1000"

Only do this changes after you upgraded your firmware to version 20180930 or higher.