Look at the picture above, we have the flap of the envelope. We need to put a letter in the envelope, some glue on the flap, bend it down and stick it to the envelope.
Normally, we need to glue the flap if we send the envelope by post. However, in some situations, we don't need to glue the flap and we just bend the flap down if we give the envelope directly to someone by hand not by post.
If I "tuck the flap in", the flap will be inside the envelope. But I don't want that as I just want the flap to be bent down. It may stick out a bit because it is not glued, but that is ok.
Is it correct to say "you just need to tuck the flap of the envelope down and send it to your boss"?
I am not sure "tuck the flap down" is correct?