The end goal when undergoing this endeavor is to make the dog enjoy and initiate playing fetch. This is closer to classical conditioning than to operant conditioning.
Clicker training, and positive reinforcement training is about operant conditioning, you condition you dog, through positive reinforcement, but the dog has to think his way to get the reward. Subsequently he “figures out” what actions are “good”.
Classical conditioning is about innate responses to stimuli. It is in a sense more “primitive” and bypasses any kind of reasoning the dog might have. When you take its food bowl he just gets hungry, there is no reasoning involved. This is opposite to the operant conditioning where you make the dog think, eg. for all the basic cues (sit, down, etc.).
In a way you want to play fetch with your dog so that he enjoys it. This is not to say that dogs don’t enjoy what you train them to do, but here we want a very “primitive” reaction, you take the toy and the dog, without thinking, starts playing.
Another thing to try is, at first to get your dog to bring the toy to you from a very short distance. Just drop the toy, back up a bit (start off with one step or less), and encourage your dog to come to you. If he does, reinforce that decision (click and treat, just treat, play tug, etc).
If that’s too much right now and your dog runs off, start in a small space (bathroom, closet, corner) where the dog can’t run off and self-reinforce. You can even do this sitting and simply ask for a hand-touch.
As your dog gets more confident, slowly increase the distance after you drop the toy. Allow the dog more freedom to make bad choices, while reinforcing the good ones.
Eventually, you can play games such as running all around the yard or house with your dog chasing you with a toy. If he drops the toy, end the game and try again. When he catches up to you, have a party and play tug / give treats. Try doing this with different toys and things.
Eventually you’ll have a dog who loves bringing you things. Now it’s time to continue back-chaining. Start with dropping the toy on the ground and letting your dog pick it up to play the chase game.
As you progress, increase the distance you’re throwing the toy and pretty soon you’ll have a dog who runs out with enthusiasm, and immediately runs back with the toy. Remember to only reward average or better responses and not to compare your dog’s “average” to others.