This form allows you to completely configure your DSR options.
Enter your preference for smoothness (how soft the image will be after downsampling) or leave it at the default.
Enter your native resolution and all of the desired resolutions you want in DSR. You can add up to 10, but DSR will not accept more than that. You do not need the custom DSR tool to get 10 resolutions if you use this method.
When you're done, press the "Get Hex" button and the data you need for the registry will be generated. Copy that and replace the "SmoothScalingData" in an exported registry file and then import.
A more detailed guide can be found here