[2022] Folding stocks

Hi I know this is a basic question but anyone know what's the key binding for unfolding a weapon stock?

so i watched some tutorials online (as the game does not provide any) I found out that some weapons (like Ump-45) have a folding stock that is folded on default but in the tutorials that i watched the guy had it unfold and i tried to find the key bind to it but there is not such a thing in the controls so as embarrassing as it is i have to ask it here. (i know it's not a big deal but the etch is killing me)