Members can request their own line of authority
here. Note that it's not all automated. In some cases some manual research may be needed.
I can't imagine the church allowing members to look up other member's LOA. So I don't know what purpose an app would serve.
Have you searched the
Help Center? Try doing a Google search and adding "site:churchofjesuschrist.org/help" to the search criteria.
So we can better help you, please edit your
Profile to include your general location.