FEATool Multiphysics version 1.13 now supports recovering/un-deleting of the "last" deleted object or objects (as in for the geometry object(s) the last delete operation was performed on).
To such recover deleted objects first ensure no geometry objects are selected or highlighted (in the
Selection listbox) and then press the
Revert/Undo. Press "Yes" at the question prompt asking whether the last deleted objects should be restored.
https://www.featool.com/doc/geom.html#op_undo