Thanks for posting here in the Community. Let's see what we can do here. To confirm, are you referring to the notification ringtone of your phone when someone presses your Nest Doorbell or the ring from your chime box inside your house? Do you have the mechanical or electronic chime? In addition to standard Nest Doorbell tones, seasonal Nest Doorbell themes are available around some holidays. You can change the theme or set a different chime sound in the app’s Nest Doorbell settings. When you turn on a seasonal theme, a unique sound greets visitors when they ring your Nest Doorbell. After the holiday, your Nest Doorbell automatically goes back to the default tone, and the seasonal theme disappears in the app. In case you have an electronic chime box inside your house, check it if there's a setting or button that you can press to change the chime tone manually.
Let us know how it goes.