To link a Group to your Facebook Page, you need to have admin access to both the Page and the Group. And if you have both try the below-mentioned steps to link your page to a group:
1. First, you will need to add the Groups section/tab to your Page so that people who view your Page will see Groups you've attached.
2. Once the Groups section has been added, navigate to the Groups section of your Page.
3. To Link, a Group, Select " Link Your Group"
4. Choose the Group you want to add to your Page. Once you click " Link," you will be redirected to the group as your Page and an admin.
and if you are not getting the option, so there is chances that the option is not available for your account yet.