You put a line of text in the mobile UI that says "To see tooltips, press and hold on a button." You can stop showing that line of text once they've shown a to

You put a line of text in the mobile UI that says "To see tooltips, press and hold on a button." You can stop showing that line of text once they've shown a tooltip (or two, if you're worried about them triggering it accidentally and not knowing how they did it).