How can I fix oven door?

I have a Diplomat GD 60 a DL gas cooker ADP 5164 Green I am having problems with large bottom oven door,the catch screws have become loose ,in fact one has fallen off and I cannot get a screw to fit .The remaining screw is coming loose.Can I rectify this problem or will I have to get a new door?If so can you tell me where I can get a replacement door and what it will cost