NURBS > Merge Surfaces combines two or more patches into a single patch. When merging patches, it is important to ensure the selected patches form an ordered array structure. This means the patches must create a logical grid formation with the same number of patches both across and down. This also means the patches must not cross degree-3 corners. Once patches are merged, the new patch cannot be merged with other patches.
To use this tool, check the Spline Boundaries checkbox in the Primitives Manager to make individual patches visible, use standard selection tools to select the patches to be merged, then click NURBS > Merge Surfaces.