A regular Enchant Relic applies a random regular enchant at Keeper's Altar. The altar works at night, the target rod must be equipped, and the relic must be held when you interact. Another roll normally replaces the current regular enchant.
Confirm You Have a Regular Enchant Relic

Check the item name before traveling. Fisch contains multiple relic types and quest uses; this guide covers the regular Enchant Relic used for ordinary rod enchanting. Keep the relic in an accessible inventory slot.
Reach Keeper's Altar at Night

Travel to the Statue of Sovereignty, enter the mine, find Cole, and take the elevator down. The documented normal elevator fee is 400 C$ unless the account has permanent access. Wait for night because the regular altar does not activate during the day.
For a landmark-by-landmark route, use the Keeper's Altar location guide.
Equip the Rod Before You Interact

Equip the exact rod you want to change, then hold the relic. Read the rod's existing enchant first. Interact once and inspect the result before spending another relic; repeated rolls can replace a useful outcome.
Treat the Result as Random
Do not plan around receiving one named enchant from one relic. Decide in advance which kinds of result solve the rod's problem and which results are acceptable stopping points. A temporary rod rarely justifies a long reroll session.
Fix an Altar That Does Nothing
Check the time, altar location, equipped rod, held item, and relic type in that order. If they all match, rejoin once and try again. The Enchant Relic troubleshooting guide separates setup mistakes from possible server issues.