Your cooker may disconnect from bluetooth for a couple of reasons:
Bluetooth has limited range - sometimes as low as 10 feet when there is significant signal interference. This can come from larger or thicker walls, or wall materials on the wall such as plaster, etc. Move your phone closer to the cooker and the two should reconnect automatically.
Your phone may have its bluetooth setting disabled. If so, enable it from your phone's settings and the two should reconnect automatically.