If the player has defeated Argo and his champion, then they can resurrect him for a number of souls at the Purging Monument. This will allow them to rejoin the covenant and continue to level up its ranks, although reentering the church will make him hostile again.

How do you revive a Halflight Spear of the church?

Halflight, Spear of the Church is found in The Ringed City, inside the church down the Ringed Inner Wall bonfire shortcut. After beating this boss, the player can use souls to revive Argo and repeat this fight. He can do it at the Velka's Statue or Purging Monument.

What is judicator Argo?

Judicator Argo is a NPC in Dark Souls 3 and a recurring miniboss. He is part of The Ringed City DLC.