You can go into YouTube studio, select the video, then go to "copyright" ... click the three little dots connected to the claim, and then "dispute." From there,

You can go into YouTube studio, select the video, then go to "copyright" ... click the three little dots connected to the claim, and then "dispute." From there, select "public domain" or whatever is applicable. It's kinda buried, but occasionally I get claims for songs not even in my video, so I had to go digging for it. Also, make sure you're using the video from 1927, and not a later release which may have a different copyright.