How to use Braum's poro dungeon passive?

[Harrix]

So as the title says, does anyone know how to use his poro passive in dungeons? The tooltip says the little guy can squeeze through areas that are too small for humans, but there's no option for me to use him that I can see.

[AvivLobel]

when u travel , there is some places that if u get close it will tell u that braum can use hes poro

[Lunar Jim]

interact with holes that it can go through with braum at the front of the party