How to reinforce and straighten a fence post
Nope, there's no training the wood to work against it's grain...without cutting many slots into it. That's your only option for keeping everything mostly as-is.

Another option is to cut the post where the bend is and big-dowel on a new piece.

You can also screw a chunk of pressure-treated or cedar onto the post's top and re-screw the fence panels onto that, to then slice off the warp from the yard side. The gap at the fence isn't usually noticeable.