In this case, you can use the "Select in the Plane" option. Thus, you can quickly select and further edit the structural elements in a specific plane (for example, hall frames or platform levels). You can find this function under "Edit" → "Select" → "In Plane".
In RSTAB, you can select nodes and lines; in RFEM, you can also select surfaces and members. The plane from which the elements are to be selected can be defined by "3 Nodes" or by "Polygonal boundary". The "3 Nodes" option allows you to select three nodes of the structure of three grid points of the current work plane in order to define the desired plane. The example shows three nodes of the structure selected. When selecting grid points, please note that the currently adjusted work plane lies in the plane desired for selection. If necessary, you can adjust this by setting a new work plane or grid origin.