You can try to clean up the corrosion with a baking soda/water paste, perhaps using something like a soft toothbrush to gently scrub the affected areas after letting the paste sit there for awhile.
There is also spray-on circuit board cleaner, which is what you'd probably want to use after the baking soda.
Once the corrosion is gone, you'll be able to see any damage and get a better idea of what you'd need to repair.
Going by the photo, it looks to me like the brown cap on the right side above the W149 blew and slowly leaked it's electrolyte. Not sure if this is actually the case since there is electroyte all over the place away from that cap, but the corrosion may have spread on it's own if crumbs were knocked loose from vehicle motion and made their way to other components.
You can remove and replace the caps with new ones if you can do soldering, and you might even be able to repair any broken traces or metal connectors with soldering as well, but whether or not it is worth your while or the cost of the repair depends on the amp.
If it's a quality brand name amp, especially something old school and no longer manufactured, it may be worth the time and money to repair it back to operating condition, or at the very least cleaning up and selling as-is to someone who wants it and would repair it or pay to have it repaired.
If it's just some low-end amp (that doesn't even come close to 1000W), which is quite likely given that low-quality components usually cause these kind of failures, then you are probably better off putting any money you would have spent on a repair towards a new amp.
What's the make/model of the amp?
