To Close Mesh Voids

Select the Close Mesh Voids tool.
Turn on Perimeter Less Than.
Set Perimeter Less Than to a value less than the mesh element perimeter.
Select a mesh element.

Mesh element with mesh voids less than the set perimeter value highlighted in yellow
(Optional) Do one of the following:

Select additional elements by pressing <Ctrl+ click>.

or
Select multiple mesh elements with a selection set.
(Optional) Press <Ctrl+ click> to change a yellow highlighted void to blue or to change a blue highlighted void to yellow.

Yellow highlighted void changed to blue
Click to close the void(s) highlighted in yellow.

Mesh with yellow highlighted voids closed