Deleting a mat region

If the mat region has been defined as a boundary, hole, or control region, you must first delete this definition from .Meshing Setup (Mat Foundation)

Click the Select Mat Boundary/Region tool in the Select toolbar.
Tip: Mat Regions can be selected using the default pointer, but this tool limits the selection to only boundaries or regions, reducing the likelihood of accidental deletions of other model elements.
Click anywhere along the boundary edge of the region you want to delete. The regions is highlighted in red.
Do either of the following:

Click the Delete tool in the Standard toolbar.

or
Press the <Delete> key.

A delete confirmation dialog opens to verify you want to proceed.
Click Yes.
CAUTION: This action may not be undone.