Some people are having trouble with it right now but if you have a mobile target account you can do it on your phone. You use your browser on your phone not the mobile app and sign in with your phone number and pin. Once you're in your account you add the physical and egift cards and you can then click on the individual cards and click on combine to add the balances together. Click on the physical card first if thats the one you want to keep the funds on.
Thanks! that worked out great!