How do i change the bid on an active manual ppc campaign

To update the bid of your Manual Targeting advertising campaign, click on the box under “Keyword bid”, type in your revised bid and click save.

You can also view the instructions in a form of an Amazon Seller University video here:

https://sellercentral.amazon.co.uk/learn/courses?ref_=selleru_athena_c147_m606&courseId=147&moduleId=606&modLanguage=English&contentType=VIDEO&videoPlayer=youtube