Where do I submit the MSL code to free my iphone from Sprint carrier

Where do I submit the MSL code to free my iphone from Sprint carrier? I have contacted Sprint and they verified my serial number/IMEI/MEID is "free and clear" now and gave me the phone's MSL Code. I was told that I had to connect it to iTunes and reset the phone and somewhere I would get a prompt/request for the MSL code but so far.. that has not happened. Can someone please help me with this...? It should be such a secret.

Phone: iPhone 4s white

IOS 7.1

Thanks.