The SELCO Libraries App is no longer functional. It was developed by a third-party vendor who stopped supporting it and shut off access to it. A replacement app is in the works, but it may be several months before it is ready to roll out.
In the meantime, you can always access your account and library catalog on your device by visiting My Library Account under the Library Catalog tab. You can also add these pages to the Home Screen of your device by tapping the square with an arrow (iOS) or the ellipsis (Android). For a video on how to do that, tap here. SELCO has also put together an Accessing the Online Catalog from Handheld Device Cheat Sheet.