Hello community, I faced the same problem with Samyang 12mm f/2. These are prime lenses without autofocus (Samyang / Walimex / Rokinon / Meike ...). EXIF data misses "lenstype", "lensmodel", "FocalLength", "ApertureValue", "FNumber" and so on. So I digged into it and here is my solution:
Use exiftool to modify the EXIF data of your raw file, e.g.
exiftool.exe -overwrite_original -lenstype="12mm F2.0 NCS CS" -lensmodel="12mm F2.0 NCS CS" -FocalLength="12" -ApertureValue="8" -FNumber="8" FILENAME
All parameters seem to be interpreted by Affinity Photo. lenstype or lensmodel must match the model tag in the lensfun db. FocalLength must match the focal parameter in the lenses calibration section of lensfun XML. Maybe also the aperture value is interpreted by Affinity Photo. Not sure about that. Once you have matching parameters, the correction profile is applied automatically. However the mapping is interpreted by Affinity Photo algorithm, nice feature would be the user could force the selection via a simple menu maker > model > mount.
Kind regards,
Torsten