STEP 1: GET DOG INTERESTED IN TOY
The easiest way to get the dog interested in a toy is to slowly move it around while encouraging him to grab it. The moment he grabs it pull it around and move it a bit, basically play with the toy and him.
STEP 2: CLICK FOR GETTING A TOY
Once you can get to grab a moving toy try requesting him to grab it while it is not moving by just showing him, the moment he grabs the toy click and treat him.
STEP 3: INCREASE HOLDING TIME
Once you can get him reliably to grab a toy, gradually increase the amount he needs to hold it in his mouth before getting a click and a treat.
STEP 4: MOVE AWAY FROM THEM
Throw a toy near you then when a dog grabs it start running backward away from the dog while encouraging him to follow you. The distance he needs to pass before you click and treat should also be gradually increased.
STEP 5: FETCH
At this point, the dog should be able to bring a toy when you throw it to him. It is a good exercise for the dog and a fun time for both of you, keep playing with him and enjoy your game :). You can always pull the toy when he brings it to you which keeps things interesting for both you and the dog.