Some devices can only be synced with one device at a time.
If you connected the JBL to another device, go to that device's Bluetooth settings, remove it, and then try connecting it to your computer again.
Also check in Device Manager if it's still connected.
Click the Start menu and type Device Manager.
Click View Menu > Show Hidden Devices.
Expand Bluetooth > if the JBL appears, right-click to remove it.