The Summon Greater Demon spell is especially effective when the summoned demon's true name is known:
At the end of each of the demon’s turns, it makes a Charisma saving throw. The demon has disadvantage on this saving throw if you say its true name.
However, the spell description doesn't say that it is possible to request a specific demon for which the true name is known:
You utter foul words, summoning one demon from the chaos of the Abyss. You choose the demon’s type, which must be one of challenge rating 5 or lower, such as a shadow demon or a barlgura.
Is it possible to request a demon for which the true name is known?