Add origin to a 3d scanned file

I scan some part, just to have the general shape. Not for retroingeneering, i use only the 3d scan to know the general size to design my accessories.

My file is quite large, in STL, that i import in Solidworks in Graphic (too large to import in Solid or Surface)

From this file, i need some planes to be able to stick my new part.

In attached, file Nr 1, the STL imported
File Nr 2, the 3 plane i wisch

This is a reccurent job, i have 1 to 5 every month.