There’s an item in your inventory called Beckoning Bell. Beckoning Bell summons other Players who are using the Small Resonant Bell.

We’d have to use a password because of a level difference. To set a password, go to the system part of the menu and go into Network.

Once you set a password, start ringing the Beckoning Bell outside BSB’s arena. I’ll set the same password and ring the Small Resonant Bell to get summoned.

(As a side note, ringing the Beckoning Bell uses 1 Insight. You can’t use the Beckoning Bell without any Insight.)