You can find the Access Control under Retailers in the main menu.
In this section you can manage access rights for retailers.
Under Open requests you will find new requests from your resellers that are still unanswered. Select the products for which you want to grant access rights to the retailer and finally click Grant all selected. You can also reject the request if you don't want the retailer to have access at all. You should decide about the requests listed here every 1-2 days.
In the My Retailers section you can find the settings for the access rights of connected retailers. If you want to change access rights for specific retailers, you can do so in this section. Click on Edit rights, set the checkmarks accordingly and finally click on Save rights. You can easily find newly added retailers by sorting by date.