I had run out of fuel at 1000 ft approaching Heathrow and I couldn’t find any emergency fuel button.

I also tried searching for it when I had only 4 minutes of fuel left but I still couldn’t find it.

Please help me!V

Have a look here at Tyler’s message. Exact criteria for a fuel emergency aren’t disclosed and you will only have the option to communicate this in the Expert Server.

I am on the training server

Okay, in this case there won’t be any way for you to communicate an emergency fuel situation then. This is reserved explicitly for the Expert Server.