I don't have your scope, but the procedure is pretty much the same for any of them. I do this same measurement with my ancient Rigol DS1202CA.
Key up a CW waveform with your scope on auto trigger and adjust your vertical volts/div so the trace fills about 1/2 of the screen.
Change the trigger to normal and set the trigger level a little above the top of the steady state waveform.
Set the scope to single shot and key up. You'll get one sweep that shows the beginning of your transmission. If you don't get anything, lower the trigger level until you do.
Play with the horizontal time/div as required.
I don't know what you mean by "record it and play it back". Just screenshot it once you have the single capture.
And of course make sure to use an appropriate RF attenuator or RF tap so you don't blow up your scope.