In D&D 5e Paladins swear an oath to an ideal not a deity.
From the Player's Handbook:
A paladin swears to uphold justice and righteousness, to stand with the good things of the world against the encroaching darkness, and to hunt the forces of evil wherever they lurk. Different paladins focus on various aspects of the cause of righteousness, but all are bound by the oaths that grant them power to do their sacred work. Although many paladins are devoted to gods of good, a paladin's power comes as much from a commitment to justice itself as it does from a god.
Paladins train for years to learn the skills of combat, mastering a variety of weapons and armor. Even so, their martial skills are secondary to the magical power they wield: power to heal the sick and injured, to smite the wicked and the undead, and to protect the innocent and those who join them in the fight for justice.
A paladin is a living embodiment of an oath—a promise or a vow made manifest in the person of a holy warrior who has the skill and the determination to see the cause through to the end. Some paladins devote themselves expressly to protecting the innocent and spreading justice in the world, while others resolve to attain that goal by conquering those who stand defiant and bringing them under the rule of law.
If you wish to imagine your Paladin serves some deity or gets their oath from some supernatural being there is nothing in the game that's stopping you.
Nothing is limiting your imagination.
If for some reason you
have to have it on your character sheet you could always type it in your name field. For test purposes I just created a character named "Tav, servant of Helm"(You only have 20 characters so choose wisely)
