FDTD uses FDE as the mode source solver, so there is no need to import data from FDE to FDTD. Thus its dataset format is not designed to do this. FDE dataset has no wavelength data but FDTD needs it. If you really want to import, please follow this example https://optics.ansys.com/hc/en-us/articles/360034383054-Using-an-equation-to-define-the-spatial-field-profile-of-a-source-in-FDTD
Basically you need the following script to create source data for import:
EM = rectilineardataset("EM fields",x,y,z);
E and H are 4 dimensional matrix, even if one (source normal direction such as z) or two (z and frequency) has only one value.