Octavia 2l tdi cupa egr cooler bypass what is needed and how to do it ?

Hi ive got a build up of black soot in the coolant tank and getting pressure in the system when taking off the coolant tank cap in the morning when engine is cold it still releases a heavy hiss of air escaping, also when turning ignition on or off get a gurgling sound from behind dashboard.

Im hoping this is a broken egr cooler and not the head gasket so to check i want to bypass the egr cooler , the dpf and egr are already mapped out .

As anybody on here bypassed the coolant pipes on the egr cooler on here before ? If so what size pipe do I need ? Is it possible to do from top of the engine or do you need to get underneath it ?