Setting the Value$ to "" seems to work for me.
print '4D','B?','CS',
rb=10
radio_button rb:1,@(10,10,10,1)="One"
radio_button rb:2,@(10,11,10,1)="Two"
radio_button rb:3,@(10,12,10,1)="Three"
button 11,@(10,14,10,2)="Reset"
while 1
obtain (0,siz=1)'ME',*,'MN'
if ctl=4 or eom=esc then break
print "Ctl ",ctl," received"
if ctl=11 then rb'value$=""
wend
I can select any of these buttons and then press the Reset to clear.