You need to add a basic skeleton to your mesh and weight paint it.
For example if you have only a static mesh (no bones) then in object mode do Shift + A → Armatures → Uefy Script → Reference Skeleton → Basic Posing Skeleton.
This will add a prebuilt skeleton into the scene. Rotate/Move the bones into you mesh and use automatic weight painting. Then manually update/fix the weight paint in problem areas with blender’s built in weight painting tools.
At this point your mesh will be just another character with an initial skeleton that can be rigged with uefy + rigify combo following the tutorials for use in UE5.
I did an older video for the lite edition for rigging a static mesh ( How to rig a character from Blender to UE4 with Uefy Script v1.3 - YouTube ) where I handmade the entire skeleton before using auto weights. But with the basic posing skeleton in Uefy 2 you can skip that and get straight to skinning weights.