I can see why current board builders have stopped contributing with advice like that but it's a forum and everyone can contribute and of course people will do different methods.
No injection of resin needed, it's a crack in the glass and the foam sandwich looks intact.
Where the foam sandwich is buckled which I did to one of my boards learning to forward then over rotating and buckling 6mm H80 foam then it's a major repair!
Years ago, I've built hundreds of sandwich boards and these days most of my resin work is on my mates sailing cat.
Is the crack in between the foot straps and the mast track caused by flat landing jumps?!
Then you need to glass so that the glass doesn't go across but is angled at 45 degrees and just past the foot straps and mast track.
Sand the paint off, glass the patch, bog the patch, fair in then paint, job done