Hi there,

Now download your wallet, go to Debug console and type importprivkey 'Your Private Key' to import your address. But since you already have the wallet, you have an address generated already, you can get a new one by going to Receive addresses and clicking Add.
Also you can find your private key that is linked to your wallet's public addresses by going to Console and typeing dumpprivkey 'Your Public Address'.

Hope this was useful.