I couldn't find any code related to disconnecting the device when its already connected.
Try BleManager.cancelDeviceConnection. https://polidea.github.io/react-native-ble-plx/#blemanagercanceldeviceconnection
BleManager.cancelDeviceConnection
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Try
BleManager.cancelDeviceConnection. https://polidea.github.io/react-native-ble-plx/#blemanagercanceldeviceconnection