Hi,
If you want to inject JavaScript to SharePoint site using Provider Hosted add-in, please check the article below:
https://social.technet.microsoft.com/wiki/contents/articles/36954.sharepoint-2013online-javascript-injection-using-embed-javascript-pattern.aspx
Or I suggest you provide more information(some code or screenshots) for further research.
Best Regards,
Dennis
Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact
tnsf@microsoft.com.

Click
here to learn more. Visit the dedicated
forum to share, explore and talk to experts about Microsoft Teams.