how to get refresh token in google oauth code example

Example 1: google oauth2 does token change when refresh

The Google Auth server issued Refresh tokens
never expire — that's the whole point of the
refresh tokens. The refresh token will
expire (or I should say become unauthorized) when the user
revokes access to your application.

Example 2: google apis does refresh token chage

The Google Auth server issued Refresh tokens never expire —
that's the whole point of the refresh tokens. The refresh token
will expire (or I should say become unauthorized) when the user
revokes access to your application.

Refer this doc it clearly states the function of refresh tokens.