Enclosure error for an STL file

I am trying to do a wind simulation on an Aerolid helmet. I keep getting this error message
No solid region could be used to create the flow volume. Please make sure to select solid regions or try to thicken or extrude sheet bodies to make them solid.
I imported the file as an STL. Does anyone have a solution?
Here is the link https://www.simscale.com/workbench/?pid=5856710225842019945&mi=geometry%3A1&mt=GEOMETRY

Hi there, thank you for using the forum!
It is recommended that you export your models in Parasolid or STEP, as STL is not suitable for this type of analysis. Is it possible that you export your model in these two formats, and re upload it?
Also, make sure to read more about CAD preparation & upload here:

Best regards,
Fillia