Read a random firebase document

I use Firebase as a matchmaking database but i would like to limit the traffic as much as possible.

I find a way to limit the “write” count (the game upload the player team stats once per 24h) .

But every time a player launch a new match the ennemy must be different, so each time, the game have to “read” the database .
So i would like to know the most efficient way to find a totally random document from a firebase if possible
( With as few “read” as possible).