Serious damage to a section of aluminum siding calls for replacement. This can be problematic if your siding manufacturer is no longer in business, which is often the case with sidings installed 30 or 40 years ago. If you can’t find a perfect match, consider stealing a piece from an inconspicuous place, such as the back side of the garage, and replacing that piece with a compatible but inexact match.
1) Using tin snips, make a vertical cut at each end of the damaged piece. Then cut horizontally along the center of the piece.
2) Leave the nailed upper section in place, and remove the lower half.
3) Cut the nailing tab off the top of the replacement piece.
4) Spread butyl gutter seal generously along the upper nailed section.
5) Fit the lower replacement piece into place, and press it firmly into the gutter seal.
6) Caulk the joints with silicone caulking compound or butyl gutter seal.
If you feel this job is too much to handle yourself, you can always get a quote from a local siding contractor.