I suppose you meant reducing the speed instead of how to combine 144 Hz with 4k.
If so, it can be done in the Windows monitor settings. This tutorial tells how to make an 144 Hz monitor run at that speed instead of 60 Hz, but obviously you can choose any speed in between. A similar setting can be found in the Nvidia control panel as well so most likely there's a drop down menu also in the AMD controls. Just set the maximum speed you want.
As to AMD, the in driver settings for monitor Hz (60, 90, 120,144, etc) has been absent since the new Radeon Settings control panel and maybe since the last iteration of the old CCC as well. This is set in Windows only if using AMD Radeon Settings. You can set monitor resolution settings (1920 x 1080, 2560 x 1440, 3820 x 2160, etc) in Radeon Settings, but not monitor Hz.
Hope this helps.
PS....If you have access to the monitor's control panel you can set both the monitor's resolution and Hz from there and Windows should recognize it.....