Put him there when he is tired and sleepy. Give a biscuit, close the door, and start pottering around in the same room - dusting is good or something similar where you are making calm movements, the puppy will start watching you and will fall asleep. Once he is awake, let him out straight away. Next time he is tired, repeat. Might take a few goes, but eventually he will associate the crate as a place of calm. Job done!
I do this with the puppies we breed, once they are about 3 weeks old they go into the crate every time I need to clean their puppy pen. The crate is in the same room, first couple of times they whine a bit and want to get out, then they become interested in the crate and different blanket there, they might play in there a bit, or they watch me clean the pen and fall asleep. Once I finished cleaning, I let them out. By the time they are ready to go to their new homes, they love the crate