Hi
You can't! First of all
make sure which version of MGO you would like to get! Ethereum or Waves MGO? Then
create a wallet from above of them and make sure the Privete keys or seed are in your full control. It's almost done!
Log-in into crowdsale
website. Put your address in available withdraw option of your  prefarence. You can be a proud
owner of both as well. In these case your available MGO
against investment will be
divided by same ammount of both version MGO!

Thanks!