Door advice + storage tray

[SamNoots]

Hi all,

Recently bought a 2010 Qashqui Acenta and love it but yesterday I was driving and constantly getting a warning that the passenger front door was open when it most definitely wasn't. I found that the door striker loop was loose, making the door not sit flush to the body. Whilst tightening the screws the nut on the inside of the door column shifted and moved away from the hole. Does anyone know how to get to the inside of the column so I can repair this properly?

Also the car came with a tray loose under the front passenger seat and I cant quite see how it fits securely under the seat, or does it just sit on the floor?