aid!!!

Hello, everyone:
my name is Juan, I am new in the forum, although I have been following you for a long time, and now that a problem has emerged, I have decided to register if you throw a hand.
I have a renault 19 GTX 1.7 My problem is that for 10 days or thus the carburetor has had a loss below the Don injection membrane where there is a drill with a golden plug without notch for screwdriver or special key. The 1st time after disassembling and changing injected menbrane I discovered said plug and when I press it in the inside 5mm and the loss was solved.
My question is as follows: would someone tell me the task and work of this plug? What repair do you need?
Sorry for the sermon, greetings and thank you very much for your time (attached file with photo)