Your lock can appear out of range for a number of reasons. hello
The first thing to try is to turn off and back on Bluetooth. The method to do so will vary depending on your phone. Look for a Bluetooth icon (), usually, it will have a blue background. Tap it once to disable it, wait a few seconds, then tap it again to re-enable it.
On iPhone, this can usually be achieved from Control Center by swiping your finger from the bottom of the screen, but you can refer to this article or watch this video. On Android, this is usually achieved by swiping your finger from the top of the screen, but refer to this article if you need further help. Note on Android, you will also likely need to enable the Location feature.
Once done, if the problem persists, you should check that you have given the app all the required permissions. This can be done in a different way depending on your operating system, refer to your OS manual for further help. On Android, you will likely need to give the app Bluetooth and Location permission, while on iOS Bluetooth is enough.
Once done, if the problem persists, you will have to restart your phone. This is generally achieved by depressing the power button for a second or two and validating on the screen that you want to power off (or restart) the phone.
Once done, if the problem persists, you should replace your lock batteries.