After completing the first Letter from Volcano Manor, talk to Patches and get Letter to Patches.   (For details: Tanith Questline)

Open the map and go to the red mark position.    Select Yes.

After defeating the boss - Great Horned Tragoth, we got the Bull-Goat suit.

Great Horned Tragoth - Elden Ring Raiders

Return and talk to Patches.

Refresh the map.     Talk to Patches and get Magma Whip Candlestick.