Introduce it like it's the first time and he's never been in it before. Make sure the crate is proper sized, make it a good place to be, feed him his meals in it with the door open so he starts making good associations. Exercise before going in and ignore barking and crying. He won't like it at first but for the most part our dogs sleep the majority of our time gone, so as long as you are exercising before closing him in he should settle not long after.
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