Admin approval for OneDrive attachments?

When I try to attach a OneDrive file, I get the following message:
“Attach OneDrive files to Asana needs permission to access resources in your organization that only an admin can grant. Please ask an admin to grant permissions to this app before you can use it.”

I am the admin, but I don’t know how to do it. I went to “Apps”, but I don’t see it. Help!