Google Nest Community

My Google nest just randomly started playing some sort of music out of nowhere and then before that made the sound of a cast connection but when I looked it was a black screen with a lil photo of what looked to be a phone with signal lines coming out...

I recently bought a new phone thats a newer version of my old phone but my google nest is still connected to my old phone for example when i ask it to "find my phone" it rings the old one. How do I fix this? Ive already tried factory resetting but it...