A forge is a much needed item in Valheim when it comes to crafting bronze weapons and armor.
You can upgrade the forge to allow you to upgrade your bronze weapons and armor.
The first upgrade to level 2 was via an anvil (but it may be the opposite for you).
Here’s how you can upgrade the forge to level 3 in Valheim.
You’ll need to make a forge cooler
Assuming you built an anvil to level up the forge to level 2, you’ll now need a forge cooler.
A forge cooler is unlocked when you’ve taken fine wood for the first time.
To get fine wood, you need to chop down birch trees.
Once you have the ingredients which is fine wood, copper and a nearby workbench, you can place the forge cooler near the forge.