Hi guys me again, what would be the best way of fixing this carbon bumper it's cracked through looks to be backed with fibreglass 

I would grind as much of the damage back as possible, then get a similar material and try and create a patch that matches the weave of the original part, if it needs it? If its not overly structural you will get away with a wet lay repair, i would try and use a caul plate or localised vac bag to consolidate the repair and reduce the amount of sanding to smooth the repair and match the surrounding part.