The problem seems to be in fbx-model, but there’s no way to change the model.
NavMechAgent moves it in right direction, but backwards-forward, like Moonwalk. Looks funny, yeah.
Is there any way to change NavMesh Agent face rotation?
If no, then how to change existing model in unity (maybe, change pivot or orientation) to make it move right?
He has imported an FBX which has an incorrect orientation (facing backwards), and wants it to move correctly when a NavMeshAgent component has been added to it.
Try creating a parent GameObject for your model and attach the NavMeshAgent to it instead, then just make sure your model (now a child of this new GameObject) is rotated 180 degrees so that it is facing along the Z axis of the parent object.
Ideally you want to make sure that any objects you export from a 3D package are set up so that the FBX comes in facing the right way, or you’ll always have to add a parent GameObject to fix any orientation issues.