When I try to give a model a collider, the Capsule still falls fall through, why is this happening?

Im trying to give my model (which is an imported dae. file) a collider, but my capsule keeps falling through it, why is this happening, if you have an answer to this then I would be grateful. I would upload the model, but it doesnt meet the requirements for me to upload it.

Add component to your object: Physics => Box to give it a structure. Adding a collider simply detects when something collides with it.
@stampogamer1

I tried that, but my model has some complex polygons, so when I adjust my box collider to the model, my capsule looks like its floating
@Shakarane