Looks like a I needs a special tool to get get a cover plate off, something with four pins but can’t see there is a tool out there like this, any advice…

Nah you don’t.There’s an 8mm (or 10mm if bb30) hex behind it.The ‘cover’ is the self extractor that pulls the arm off the spline.
Just undo the hex ,they can be stiff as a bugger at first.

Tried that and so far with a park tool 8mm allen key plus a 300 mm adjustable spanner looked onto it all i’ve done is bend the allen key…

A mate of mine (mechanic in a shop selling Specialized!) had this issue on the same bike! 2 month old bike, tried taking the cranks off to go 1x and bolt wouldn’t budge no matter what he tried, even with a massive leverage bar. Specialized ended up sending him some carbon cranks under warranty. An angle grinder was used in the end to cut the old cranks off.

Yes they can be very tight and when you loosen them they can go with a bang and a cloud of dust .

MOAAR POOWWER!!

Maxed out on power so went the leverage route, tried an old pair of 680mm bars over the now slightly bent allen key, no joy. So stepped it up to some 750mm bars and…CRACK! The noise made think something had broke but it was just the allen key bolt surrendering grip, my ears are still ringing…
So If you do the same job on your Camber, get some ear defenders!

Heat is your friend here, even a kettle of hot water would help, just to get things moving. I had to get the blowtorch on my Zee cranks to soften the threadlock on the (OE) ring bolts 😯

Just to make sure- you are trying to undo the bolt on the driveside, not the non-driveside, aren’t you?

Theres nothing to undo on the non driveside on these cranks.