Can you change the bids of keywords once they have been created in AdWords or Bing Ads?
You may change the keyword bids after the campaign has been submitted live to your search engine advertiser account by going to the Optimize section of the Campaigns tab, and activate a Bid Management rule.
You can also manually adjust keyword bids directly through your search engine advertiser account.
*Please note that changing the bids through the 'Set Keyword Bids' section of the Campaign Builder will NOT affect the bids of existing keywords. The 'Set Keyword Bids' feature only sets the bids for newly created keywords that do not yet have a bid.
For further clarification regarding initial bids, please see THIS article.