Trystrom has lost all of his faith in the gods. This is bad since he is a cleric. Luckily, he knows of a nearby temple that contains sacred writings. These writings are said to restore faith to anyone who reads them. Surely this has got to help. If not, he can always rediscover his faith in some other way. Here is how you complete the Clerical Error side quest in Tiny Tina’s Wonderlands.
You can find Trystrom in the Overworld near the entrance to Crackmast Cove. To reach this area, you will need to complete the Ballad of Bones quest and have the Overworld section past Wargtooth Shallows unlocked. From Wargtooth Shallows, go down the hill and make a left. Go up the hill, and you will find Trystrom at the top.
Trystrom will point you in the direction of a nearby temple where you can get the sacred writings from. Go down the hill and under the invisible bridge to the Temple of Faith. Enter the dungeon. You will have two waves of enemies to defeat inside. The first wave will be Coiled, and the second will be Seawargs. Once you complete the second wave, you will obtain the sacred writings from the reward chest. Return the sacred writings to Trystrom, and the quest will be complete.