Set up a routine. Mine learn to stand on a grooming table and I'll just reward that and maybe do a few swipes with the brush. they also get use to being restrained by a grooming loop, though after I while I don't have to use it anymore. Baby steps are key. You will NOT be able to do a full brushing at first, maybe a minute or two and then quit while you are ahead or else it becomes a battle and both you and the puppy hate it. If you really need to work on something get help, someone to distract and feed or else wait for you pup to crash and brush while they are sleeping/sleepy.
My GSD loves to be brushed. As a pup he did think it was a game, but he got past that once he learned what I wanted.
If all you have is a hammer, everything looks like a nail.