uncheck Radio button

You're correct, but this would apply as long as the radio button group is mutually exclusive (same field names but different export values; will make the radio buttons behave like checkboxes independent from each other), otherwise the whole group of radio buttons will be checked or unchecked in unison by tjust checking one of them alone.

When you use a group of mutually exclusive radio buttons you'll also may  need to emply a zero-based index workflow in your script(s) to work with each radio button individually.

Radio buttons are indexed in the order that they were created.

That said, if you have three of them in the same array, and each radio button has the same field name as  "RadioGroup", then  the zero based-index workflow would look something like:

this radio button is the first one in the Array --->>> this.getField("RadioGroup").isBoxChecked(0);

this radio button is the second one in the Array --->>>this.getField("RadioGroup").isBoxChecked(1);

this radio button is the third one in the Array --->>>this.getField("RadioGroup").isBoxChecked(2);

As for your reset button you don't really need a code to reset them all since you can use tha built-in Mouse-up event "Reset a Form" and just select from the picklist which radio buttons you want to clear..

But if you still want to use JavaScript you can do the same as a Mouse-up javascript action with:

var f = this.getField("RadioGroup");

this.resetForm([f.name]);