Once you are done, you can come and interact with Gurranq. Once you start the interaction, he will ask you to bring him deathroot. Deathroot is a rare collectible item that you would find across the map. Once you find deathroot, be very careful with it, as it is a rare item.
Also read: Elden Ring Sellen Quest Location
Below are some of the locations where you can easily find Deathroot
You can find Deathroot in the chest after defeating the Ulcerated Tree Spirit boss inside the Giants’ Mountaintop Catacombs (Mountaintops of the Giants).
You can find it inside a chest behind the Red Wolf of the Champion at Gelmir Hero’s Grave (Mt. Gelmir).
You can find Deathroot inside a chest after defeating the Stray Mimic Tear in the secret catacombs underneath the Hidden Path to the Haligtree (Mountaintops of the Giants).
Get Deathroot, post defeating the Tibia Mariner on a ledge between Castle Sol Main Gate and Snow Valley Ruins Overlook (Mountaintops of the Giants).
Get Deathroot in a chest behind the Black Knife Assassin in the Deathtouched Catacombs (Limgrave).
Get Deathroot inside a chest behind the Cemetery Shade in the Black Knife Catacombs (Liurnia).
You can find Deathroot defeating the Tibia Mariner at Summonwater Village (Limgrave).
Get Deathroot after defeating the Tibia Mariner at Wyndham Ruins (Mt. Gelmir).
You will find Deathroot after defeating the Tibia Mariner at East Liurnia of the Lakes (Liurnia).
How to deal with Gurranq?

Usually, the Gurranq seems very passive but when you give him the deathroots, only give him 4 and not more than that. After giving him the fourth deathroot, you can rest at the site of the grace and wait for Gurranq. While you are in the site of grace, be prepared as Gurranq will try to attack you followed by a deadly loud scream.
Most importantly, be calm and keep dodging his attacks as you would not want severe damage being caused. Once you see a chance to attack, take it and hit for 1000 damage. This would make him passive again. Be careful while dodging Gurranq’s attacks, or they can really land on unexpected. The fight is not a difficult one to win tho! Once you’ve defeated Gurranq, he would serve you with additional rewards. Continue feeding the remaining Deathroots to Gurranq, you will need a total number of 9 deathroots for the quest.
All 9 of them have to be acquired from the places mentioned above.
After you give Gurranq the last deathroot, he will say that his hunger has still not been satisfied, but he will anyway reward you with the Ancient Dragon Smithing Stone, which is a pretty cool stone as it can strengthen up armaments up to +25. And here’s the list of rewards for each deathroot.
6 Deathroot – Stone of Gurranq (Incantation)
7 Deathroot – Beastclaw Greathammer
8 Deathroot – Gurranq’s Beastclaw (Incantation)
9 Deathroot – Ancient Dragon Smithing Stone
5 Deathroot – Beast Claw (Incantation)
4 Deathroot – Ash of War: Beast’s Roar
3 Deathroot – Bestial Vitality (Incantation)
2 Deathroot – Bestial Sling (Incantation)
1 Deathroot – Clawmark Seal