The general solution here is to add the site to the list of IE-only sites. This is a group policy that can be applied to all computers or a subset as needed. This is the recommended approach such that once you have updated the app to work in Edge then the IT team can remove the configuration and users will suddenly be able to use Edge.
You can find the steps here. Note that IE mode was/is a temporary solution so you're going to need to update your app before it is finally removed.