How to add money on a gift card that was pre-purchased before gift card was present

[SalonMysa]

So before my gift cards were got to my salon o had someone want to pre purchase them. I colelected the money and I would send when gift cards got sent to me. I now have the gift cards but I don’t know how to add monetary value to it with out making a new charge.  I also would like to know this answer because I will be donating a gift card to a charity and want to load it with value as well from my business 

[VanKalkerFarms]

you can load the cards with "cash" but apply a 100% discount to the transaction.

so say its a $100 gift card, load the gift card with $100 like normal. then apply a 100% discount to it so the transaction will be for $0.  complete the transaction to fully load the card.  now you have a $100 gift card that you didn't have to add the $100 a second time to Square.