One way you can reduce the vertex count on your mesh is by using the Decimate modifier in Blender.
Applying the Decimate modifier to your mesh
First, you'll want to select the mesh/submesh you want to lower the vertex count on. You will know it is your active selection if it is highlighted in yellow, and not orange.
Next, at the bottom right, click on the blue wrench icon to go to where you add modifiers.
Click 'Add Modifier'
You can find the Decimate modifier here:
Once it is added, you can lower your vertex count by dragging down the ratio slider. Check 'Triangulate' as well. Some meshes use what are called "quads", which aren't compatible with most games.
However, before you do this, it's a good idea to actually see what you're doing, so I recommend enabling the statistics overlay to see the live vertex count on your selected mesh.
It will appear to the left, beside your toolbar
Now, drag down the ratio slider till you are happy with the result.
Each mesh and/or submesh must be under 65,000 vertices to be exported to Wolvenkit
