How to retarget 3dsMax mesh to UE4 Skeleton

Hello I have an existing "UE4 mannequin skeleton " in UE5 that has existing clothing. I have found an another set of clothing that i wish to add to this system as part of the SmartPoly Survival Craft game development.
The new clothes i wish to add are just a mesh without any skinning weights or skeletal rig.
I have imported the new desired clothes meshes into 3dsMax and created a CAT rig and adjusted skinning weights.
This i have exported this to UE5 and the CAT rig is visible.
My question is how can i retarget the CAT rig to use the UE4 Mannequin skeleton instead?
I don’t have any animation. I already have animation that the UE4 mannequin skeleton rig uses. Not sure if this is an issue.
I can find the retarget manager option under the “skeleton” of the new mesh i want to use. But cannot find the bit where i remap the relevant bones to the target UE4 Mannequin Skeleton.
I did this before with a mixamo animation remapping to a UE rig but that was an animation where this time i just want to remap the meshes from the CAT rig to the UE4 rig.
Any help much appreciated.