First you need the Porsche GT America (by IER) mod , you can find it here on Racedepartement.
Then you put the folder "Frikadelli_VLN" folder it in ->"content"->"cars"->"ier_gt_america"->"skins" folder and it should be available in the Content Manager.
Sabine Schmitz drove in the 997 GT3 R by that time.
Frikadelli used in the 2015 VLN season a 997 GT3 R (SP9), the 991 GT America (SP7), later that year a 991 GT3 Cup MR (SP7), a "private" 991 GT3 Cup (also SP7) and a 981 Cayman S (V5).
You can find more infos here (unfortunately in german):
Then you put the folder "Frikadelli_VLN" folder it in ->"content"->"cars"->"ier_gt_america"->"skins" folder and it should be available in the Content Manager.