Printava used their keyword report and found that most of their keywords were performing well. However, they noticed several keywords with very high ACOS. What can they do to reduce the amount of clicks they are paying for?

Adding those keywords as negative keywords is the correct approach because it prevents your ads from showing for those specific terms. This directly reduces unwanted clicks and, consequently, lowers your ACOS for those underperforming keywords. Increasing bids would have the opposite effect, potentially leading to even higher costs and ACOS. Removing or adding ASINs (Amazon Standard Identification Numbers) affects which products are advertised, not which search terms trigger your ads, so these actions wouldn't directly address the high ACOS caused by specific keywords.