What if the phone my Apple Watch is connected to no longer exists?

My Apple Watch thinks it’s still connected to a device that has been reset and is being used by someone else. Unfortunately my daughter passed away and we gave her cell phone to her daughter and I took her Apple Watch. Her iPhone has been reset and is now being used by my granddaughter, the watch however still thinks that it’s connected to my daughters phone and will not allow me to connect it to my phone. What can we do?