Export both VTuber models from their original software in a compatible format
Import both models into a 3D editor or VTuber editing tool
Separate the body parts, accessories, and facial components you want to keep from each model
Merge the selected meshes into one project
Match the scale, position, and orientation of all parts
Combine or transfer textures into a single texture set if needed
Reassign materials and shaders to the merged parts
Check and merge the skeletons or armatures if both models are rigged
Retarget or fix bone weights for all merged meshes
Resolve any duplicate bones, blendshapes, or morphs
Test facial expressions, tracking, and animations
Fix clipping, deformation, and missing textures
Export the combined model in the required format
Import the final model into your VTuber software and test it again