After casting this spell, you can use a bonus action to expend a spell slot onto a weapon within range. When you expend a spell slot this way, the chosen weapons damage increases by the normal weapon dice damage x the level of spell expended of a damage type of your choice.

As an example, if you expend a 5th level spell slot on a longsword, it will do 1d8 slashing damage and 5d8 fire damage

This effect lasts on the weapon until the beginning of the casters next round