It sounds like you were trying to make your horse a non standard human character in 3DXchange. If that's the case you'd have to have your horse in a t-pose. Normally there is no bone config to do in 3DXchange just importing a non human character.
Hi guyoo, Can you capture a screen video about this issue, put it on the YouTube, and add the link in your next comment? Molly Reallusion
could you record your workflow you can show in private comment