You must add the +1 version of the weapon this has been forged into to your character sheet separately.

This Weapon is a +1 weapon.

At the end of each long rest you can select cold or the magical form of the normal damage type of this weapon, this weapon deals that damage type till the end of your next long rest.

Winter's Claw When you hit an opponent with an attack, you can sap their warmth. The creature must make a DC 15 CON save. On a failed save they take 3d4 additional Cold damage and have their speed reduced to 0 until the end of your next turn. On a success, they take half damage and their speed is not reduced. Additionally, you can call on the cold to protect you, when someone fails the saving throw caused by this effect, you gain half of the damage dealt as temp HP Once this feature is used it cannot be used again until you complete a short or long rest or you spend 3 minutes near a source of heat such as a campfire

Notes: Requires attunement by someone with proficency in the forged weapon.