1. First of all, this product has four surfaces, and we need to turn it into a whole surface.

2. Secondly, open the "Through Surface Mesh" command under UG 12 "Surface" menu, and construct a large surface according to its four-sided contour lines.

3. Finally, open the "Trim Faces" command under the "Surface" menu, select "Suitable for Target" under the type, and then click "Faces to Trim".