Allowing someone else to sell and power of attorney

I am currently outside the US and cannot be back immediately due to family
reasons. I have left the car in the care of my cousin and provided him my car
title with my signature. In the case, my car moves through the final stages,
would my cousin be able to complete the sale on my behalf ? And, what
documents might help make the process smoother ? And, if Power of
attorney document does help, where would I notarize such a document so
that it is acceptable back in the US ?