Thanks for posting.
Here's how to search for your Nest speakers MAC address. Click here.
Usually it doesn't show unless you try to set it up again. Do a factory reset first to revert it back to its default and original settings. Proceed with the set up. Once you get to the part where it asks you to choose Wi-Fi, stop there. Go to the 3 dots on the upper right corner and from there you will see the option to show the MAC address. Make sure that your phone is connected to Wi-Fi and not to your mobile/cellular data.
Keep us posted.