After you have already crafted a weapon in Soulframe, go to Tuvalkane and select the Reforge option (next to Assembled) to put a Joinery in it. This modifies the weapon according to the type and tier ...
As you play Path of Exile 2, you'll inevitably pick up a lot of equipment you can't actually use. Most often, you'll find equipment that's simply of the wrong type for your current character class.