Please advise how to collect checked in luggage from Du Jiangyan station arriving from Chengdu.

First of all, I wanna tell u that it is usually fine to take your luggage on China train, although u have several pieces and they are large. The staff won't care about that. But they are many cargos that required checking in. You can find them at the checked in lugagge office in certain railway station with your check-in receipt.