first, you have to find the frame difference between the two videos. Personally, I use MPC-BE and find the same frame for both videos, press ''control-g'' and calculate the frame number difference. You can navigate frame by frame with ''control left/right arrow'' when the video is paused.
Another method that could be easier for you is to open both videos with staxrip ''video comparison'' (tool/advanced) and navigate to the same frame.
I prefer mpc because you don't have to load the video like you have to do with staxrip. if your pc/gpu is powerful enough you could open two instances of MPC.
EDIT: it is no more needed to calculate the framecount since the latest update. You only need to calculate the frame difference so the rpu is in sync with the bluray remux.
this is the json for SOUL