I think the easiest way to convert to DNG is to use that conversion feature within Lightroom. You will be given the choice of whether or not to keep your original raw files, or to replace them with the DNG files. If you choose to replace then Lightroom will automatically know where the DNG files are located. If you use the DNG converter then it will be necessary for you to manually delete your original raw files if you choose to do that. And then it will be necessary for you to import the DNG files into Lightroom.