You can use Google and find more information than you've got time to read or do some or all of the following. Basically the more time you put in the better the end result.
You should flatten the surface and remove scratches and gouges first starting with a file then coarse, medium and fine wet and dry paper using WD40 or CRC to keep it cutting, finish with a metal polish of your choice and a clean soft microfiber cloth. (My words).
"You can polish your aluminum by hand or using a machine; the recommended approach will depend on the size and condition of the workpiece.
Typically, when smaller aluminum surfaces are dull but do not show significant oxidation, rust, pitting or burns, you can use a good hand polish with a microfiber applicator to give them a quick shine. If you're tackling a large object and using a commercial polish, it’s faster to use an angle grinder with buffing wheels. or fit a buff on your pedestal grinder. Industrial buffs have powerful motors and upgraded bearings to cope with high loads but you are unlikely to need to go that far.
Add a bit of coarse abrasive compound to your stiffest buffing wheel. Buff the entire surface in sections, adding more polishing compound as needed. When you've finished this step, wipe the residue completely off and change your buffing wheel, as you don’t want to mix abrasives.
As with sanding, start with the coarsest abrasive and work your way down. You can start with a gray metal buffing compound bar, which is formulated for cutting non ferrous metals and reducing imperfections, and follow with a brown tripoli, which does an excellent honing job on aluminum. For a mirror shine, finish up with a white rouge buffing compound and give the workpiece a final wipe with a clean cloth."
(copied from
https://www.redlabelabrasives.com/blogs/news/how-to-polish-aluminum-the-full-guide)
