Click Edit > Surfaces > Untrim
Click Untrim to untrim a surface previously trimmed, either once or a number of times, using surface trimming commands.
Surfaces extended using the Edit > Extend command cannot be untrimmed with the Untrim command.
Older composite surfaces can be untrimmed with this option.
Surface
The Surface command untrims every trim operation that has occurred on a surface. A surface can be trimmed multiple times to multiple elements. All these trims can be untrimmed in one step by clicking the Surface command and then clicking on the surface.
Edge
The Edge command untrims a single trim operation. To untrim a single trim, click the Edge command and then click the edge of the surface along which that trim operation occurred.