I’ll show you how.
asset, with color
Go to Shading (top-side of UI).
With shift + a, you can add a node. Add an Image texture node. Click new > ok. Make sure you select the item node.
Now go to render settings (right side of screen). Set engine to cycles. Scroll down to baking. Set bake type to diffuse. Deselect direct and indirect.
Select the mesh in the viewport. Hit bake. Wait for it to complete.
Now the image texture was baked to from the material. Make sure you save the image texture.
Upload the texture into Roblox. Add a surfaceAppearance to the mesh, and plug in the ID of the texture.