Follow these steps to add new targets to your product targeting campaigns
In the left menu, click on Product Targeting under Sponsered Ads
Click on Add product Target
Enter the targets
Select the Campaign Types, Campaigns, Ad group and click Next
Now Select the Targets and enter the bids. There are three ways in which you can enter the bids:
You can apply Amazon suggested bids. In the textbox, enter a default value when Amazon Suggested bid is unavailable for the target and click Apply
You can choose Custom bids. In the textbox, enter the custom bid value and click Apply
Individually enter the bid value for each Target
Once done and click Submit.
Watch this video for detailed steps: