On my desktop PC I hit reply and the normal reply/post window opens.
On the right of the text box are some smilies. At the bottom it says "more"
Click that and another little box opens. That box has what appears to be
one row of extra "emocons" but if you drag the side of the box right and
make it larger you can see there are actually 2 rows and the right row has
all the flags.
If you're using an ap on a tablet or smart phone I can't help ya!