2024 rules reference for Flame Tongue.
Weapon (Any Melee Weapon)
While holding this magic weapon, you can take a Bonus Action and use a command word to cause flames to engulf the damage-dealing part of the weapon. These flames shed Bright Light in a 40foot radius and Dim Light for an additional 40 feet. While the weapon is ablaze, it deals an extra 2d6 Fire damage on a hit. The flames last until you take a Bonus Action to issue the command again or until you drop, stow, or sheathe the weapon.