Fortnite save the world using force sources?

My question is how can I apply Fortnite Save the World to my sources of power I have bought in the item shop?

I thank all the helpers in advance

With the power sources you can z.b. Make an epic weapon legendary.
Example:
Epic Stormblade → becomes Legendary Stormblades.

You need to make a weapon Legendary Legendary power sources, Epic make epic power sources, etc.

To do that, go to your sketches, click on a sketch you want to upgrade and then go to "UPGRADE / OPPORTUNITY", then at the bottom right to "Equip" and then to "INCREASE FREQUENCY", and then confirm it. And already your sketch is legendary. If there's not "INCREASE FREQUENCY", the weapon is already legendary or you can't upgrade it for some reason (?).

It's every week
50 legendary power sources for 750 gold
100 epic power sources for 750 gold
200 rare sources of power for 600 gold
at the shop.