Hi,
There is no easy way to import the exported "m" file into AppDesigner. The "mlapp" file is a structure which contains metadata and XML files, whereas, the "m" file contains only the code. In order to directly import the app file, the metadata and the XML files would be needed, which are not present in the "m" file.
If you are looking to manage your .MLAPP code using Git please refer to this answer which breifly explains how we can use Git inside MATLAB.
