Honestly I'm a little confused by your question. Do you mean opening the bot in RA2 or a different software?
Assuming a different software (eg Paint to do your own skin), you need to export the skin from the paint shop (or whatever it's called) area of the robot workshop, and you can then open the output file that'll be in the Custom Textures folder of your RA2 directory. You can then import back from the same area of the workshop. :)