Find an ancient city, or locate one with '/locate structure minecraft:ancient_city'
Go to the reinforced deepslate rectangle, clear out the sculk veins, and you guessed it, light it with flint and steel.
Go through the portal you lit.
Look for warden ore, and mine it with a netherite pickaxe.
Mine three more with a silk touch netherite pickaxe.
Craft some deactivated tools with warden scales you mine.
Go back to the portal and mine the corners of it with a deactivated warden pickaxe.
Summon the warden boss with a structure like the wither's, replace the soul soil with reinforced deepslate, and replace the wither skeleton heads with the warden ore you got from mining with silk touch.
Defeat the warden boss to get the warden's heart.
Activate your tools like this:
or this:
