How to put lines into same surface

Hi guys. I m drawing line on the top view and try to extrend them. But I found out these lines do not on the same surface. Does anyone know Is there any way to put all the line on the same surface by a commend rather than by hand :frowning:

Thank you for the reply in advance !

ProjectToCPlane (option Copy off) or SetPt (untick “Set X” and “Set Y”, then “Set Points” and select an object with the desired Z-coordinate.