Set the dog crate up with the door propped open, so it can’t accidentally shut the dog in, and toss a tasty treat into the crate. More than likely, the dog will run in, eat the treat, and run right back out. Do that about five times, then take a break. If the dog isn’t particularly interested in food, you can use a toy. After playing this game three or four times, close the door but don’t latch it. Let the puppy out before he panics or fusses. Repeat this process.
Eventually, you’ll be able to close the door for a little while. Ideally, try this when the dog has been outside recently to eliminate and is a little tired. Make sure there is a dog toy in the crate when you do this. Hopefully, the dog will eventually settle down and even sleep for a while. If the pup wakes up or fusses, come to the crate but wait until he settles to open the door. You don’t want him to learn that making a scene gets a positive result! Most puppies learn quickly and want the area where they sleep to remain clean.