Fixing Models Moved into Blender

I have been having this issue for the longest time ever, I am trying to get stuff from roblox into blender so I can smooth the edges but when I do that into edit mode in blender, the models are hallow and wont smooth, how can I fix this?
image

wrong topic
u want to go to #help-and-feedback

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Arent all models hollow tho?? like they are just a collection of planes that make a solid.

What affect are you trying to achieve?