Microsoft offers a convenient way to install add-ins for multiple users at once. This is also ideal for companies that globally block access to the Office store but need to make exceptions for certain users and/or apps. 

Microsoft has an article here that describes how your Administrator can deploy specific Apps from the store to one or more end-users while still preventing access to the store for all users.

Step 1: In the admin center of your Microsoft Office 365 account, go to Settings

Step 2: Then select Integrated apps > Deployed apps > Get Apps.

Step 3: This will open the App Source page. Search for the ExtenInsights or CloudExtend app. Hit Next.

Step 4: On the next page, select Everyone, Specific users/groups, or Just Me to specify to who the add-in is deployed. Use the Search box to find specific users or groups.

Step 5: Select Deploy.

​Step 6: A green tick appears when the add-in is deployed. Follow the on-page instructions to test the add-in.

💡 Note: Users might need to relaunch Office to view the add-in icon on the app ribbon. Outlook add-ins can take up to 24 hours to appear on app ribbons.

Step 7: When finished, select Next. If you’ve deployed to just yourself, you can select Change who has access to add-in to deploy to more users.

👉 Reference: Office documentation link.