The only import plugin is available for Aperture & Iphoto to Lightroom not for Photos.
You need to export out all the Images on some location on your machine from Photo and then import the images in Lightroom from there.
else you can access the package contents of the Photos (by CMD +Clicking on the Photos) and look for the master library folder, where you have the images.
Thank you Mohit for your advice. I will follow your instructions.