how do you auto sync sound form an external recorder in primer rush
Welcome to the Rush forum.
Rush does not have a feature for automatically syncing video and audio that were recorded separately. So your best bet will be to go old school and use a clapper board--or the "handy" alternative: snapping your fingers in front of the camera. Then you can scrub to the frame showing the snap, and move the video clip so that the spike in the waveform aligns with the playhead.
You need to include how to actually move the video and sound separately so I can align them as you suggest. For me it's impossible to move them separately, both video and separate audiotrack move together. I am working on the iPad version.