So you're just trying to set your refresh rate to 60hz because it is at 30hz right now? If that's the case I would go through the settings built onto the monitor and try changing the refresh rate there. There is no reason for a 1080ti or a 4k monitor to not support 60hz.
Also try this to adjust the refresh rate in windows.
"Adjust the Refresh Rate.
1. Close all open programs.
2. Click Start, and then click Control Panel.
3. In the Control Panel window, click Appearance and Themes, and then click Display.
4. In the Display Properties window, click the Settings tab.
5. Click Advanced, and then click the Monitor tab.
6. Click the Screen refresh rate drop-down menu under Monitor settings.
7. Select the refresh rate you want from the available options, and then click Apply.
8. When you are informed that Windows will now adjust the refresh rate, click OK.
If a Refresh Rate warning appears stating that you have specified a custom refresh rate, click Yes.
If the new settings are compatible, the screen will reappear with the new settings.
9. Click Yes if you want to keep the new settings.
If new settings do not work, Windows® will attempt to revert back to the original settings automatically. If the video has become corrupted or an Out of Scan Range error occurs that cannot be automatically corrected, restart the computer. Press during startup, highlight Safe Mode from the Startup Menu, and press to start the computer in Safe Mode. In Safe Mode, change the screen resolution back to the original settings and restart normally.
10. Close all windows and restart the computer when prompted." (Dell.com)