Turn on NanoVNA.
Select desired freq range or default of 50Khz - 900MHz
From the menu press CAL
Press RESET
Then press CALIBRATE
Press OPEN with nothing connected Ch0 
Menu now moves to where it says SHORT (a light shade of green)
Connect the SHORT on CH0 and press SHORT
Menu moves to LOAD and turns a light shade of green
Connect your 50R load to Ch0 and press LOAD
Menu moves to ISOLN with alight shade of green.
Keep the LOAD connected on CH0 and press ISOLN
Menu moves to THRU in a light shade of green.
Connect a short lead (provide from Ch0 to Ch1
Press THRU
Menu moves to DONE in a light shade of green.
Press DONE
Then press SAVE 0