Sellers can sync affiliates to a new product by going to Sellers> Your Affiliates> Affiliate Sync here:
Select the product that your Affiliates are already approved to promote and then select the additional product you would like them to be approved for. Click Sync Affiliates. If you check the box to ignore Custom Commissions your Affiliates with a Custom Commission will receive the commission rate you have set for the product you are syncing them to.
This video details how to properly sync your affiliates For a step-by-step guide, you can click here to download: How to Sync Affiliates.