It is better to place profiles into ~/Library/ColorSync/Profiles/ folder (you can add subfolder here for clarity – I use Cameras subfolder for example). If you copy them into Capture One application folder as suggested, they will be removed during application update probably.
If you don't know, what is the proper filename for your camera, you can find its generic profile in mentioned folder Capture One/Contents/Frameworks/AppCore.framework/Resources/Profiles/Input. For Fuji X, these prefixes are used:
So for example, if you want to make Provia profile visible for X100S in Capture One, rename FujiXT1-Provia sRGB.icc file to FujiX100s-Provia sRGB.icc.