How can I repair the metal cover on my exterior door trim?
A siding contractor could easily make a new piece of bent metal trim for you. But the cost would probably be 150-200 dollars.

Or you can order a custom bent piece in the same style and color from trimbender online. Take careful measurements and enter them under the matching profile. Select the texture and color and your done. They will make the piece and ship it to you. Or you could replace the door trim boards wit a pvc trim board of same size from big box stores.