The new Google page has instructions on how to turn off “chat features,” which effectively turns off RCS chat. The page suggests that you can turn off chat features if you miss messages before switching to a new Android phone or switching to iMessage completely on an iPhone.
However, in case you don’t have access to the old phone because it was lost or stolen, or if you forgot to deactivate the chat features before swapping a device, you can now fill in a online form and manually disable chat features.
All you have to do is enter a phone number associated with the chat features and enter a unique code which will be sent to your phone number by SMS. Of course, you will still need access to receive text messages on your phone number.
Source • Via Reddit