Once you have opened the Mi Fit App, you need to sign into your Mi Account or create a new account if you don't have already one.
You'll also need to give the App certain permissions before you sign in and start customizing your profile.
You'll need to turn on Bluetooth so that the App can start the pairing process with the Mi Band 2. Then 'Select devices to pair' and choose 'Band' from the list.
Once the Mi Band 2 is detected, you can choose the Mi Band 2 to complete the setup process. You can then continue to customize your Mi Band 2 such as which wrist it's worn on and app notifications. You can also perform additional customizations on your profile and accounts.