Wow! Not a simple task considering how close the Nano is to the pc board.
Probably the best (easiest) way is to solder a six-conductor wire and lead that out to a six-pin connector. Color code it so that red is V+ and Black is ground.
Note that Avrdude and Avrdudess will knock out the boot loader if used to load new software. Their first task is to wipe clean the entire memory space of the mCu. You must take special pains to avoid that if you are ever going to use a USB loader again.
The square hole is pin1. The pins are stagggered, i.e., they run 1-3-5 and 2-4-6.
