I'm not sure what you mean by "turn on"? If you're referring to the physical kill switch on the laptop itself? Then it may be that this switch somehow disables the radio on both devices. In that case you want to leave that switch alone...
You don't need to disable the device. You can set network manager to use wlanX (where X is the number of the device). The other device won't be used, if it is, then you need to remove it's configuration as it's probably set up to connect automatically.
If you just want it disabled then the best way to disable the unwanted device is to blacklist the kernel module(s) it uses as follows
echo "blacklist iwlegacy" > /etc/modprobe.d/blacklist-iwlegacy.conf
It may also be a good idea, though probably unnecessary, to blacklist some of the other intel wireless kernel modules. So you could edit the above blacklist file and some other relevant modules
At this point reboot. The interface (presumably wlan0) for the intel wireless NIC should be gone.
Ensure that you have radio enabled (as if you are enabling the laptop's intel wifi). Verify this with
show the extra interface, it should only show e.g. wlan1. You should then configure network manager to use that device.