I believe the proper procedure for restoring a smooth finish where the paint has blistered and broken, is to sand an blend those areas with the remaining paint. Of course, you'll want to sand the rest of the paint you want to restore. Once that is done, prime all the bare areas and sand again before painting. Then more sanding and painting until you get the paint where you want it.
Metallic paint can be a real S.O.B. to get blended and matched. I had a heck of a time getting my windshield visor to match the rest of the truck.
All the sanding is wet sanding to keep the dust down and keep the paper or emery cloth from clogging. A lot of wiping down to remove the paint residue is also needed. Water is fine until you get to where you are priming or painting. Then I found rubbing alcohol works well for cleaning the surface and not ruining what paint is already there.
You will also need patience. Lots of it. Once you are done with a coat of primer or paint. Wait a day or two for it to cure before you start sanding again or you could ruin the finish and will have to start all over again.
Basic prep, I use 120 grit to start. Then 320. Then 400. Then 600.
Prime. Then 600. Prime again. 600, then 800.
Paint. 800. Paint. 800.
Once you get to where the paint looks good when you wipe it with alcohol (it will give you an idea what the paint will look like when polished). Then you step down to finer and finer grit (1,000 grit, 1,500 grit, 2,000 grit), stopping at either 3,000 or 5,000 grit. Then buffing with a polishing compound.
This is what I found worked for me. I am in no way a professional painter.
The pros might have better recommendations or better tips.