Just for some fun Whitney, and in real general terms, you put something in his mouth and you don't exactly take it from his mouth, but you let him release it into your hand. Patiently and calm, put it in his mouth, calmly praise, calmly have him release it. The putting it in his mouth helps show him he has to do it. Reward him calmly as soon as he releases it, move him around to relieve the stress.
Later on you expand it to him being allowed to take it, but you want to spend a lot of time on the initial place and hold. Thats kind of a thumbnail version from part of Ivan B's retrieve.