Roblox removed the surface interface recently. 
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It’s probably because the feature has deprecated.
Yep, they removed it but I think there still IS hope. Here’s some things you could try:
Type into the command line game.Workspace.YourPartHere.TopSurface = Enum.SurfaceType.Studs or something along those lines. (Again not sure)
Or you could try using the F3X Building tools plugin which has it’s own surface interface.
Lastly, you could try to look for a texture of studs and apply it?
If u change the surface appearnce, surface option will pop out in the propeties…i guess