To use MillionVerifier's API to automatically verify contacts within Google Sheets, you can use Zapier for the connection.
You can find more information about this here: https://zapier.com/apps/millionverifier/integrations.
However, you can also download your sheets in a CSV and upload them for verification manually as an alternative. In addition, you can also use our bulk API for this: https://help.millionverifier.com/email-verification-api/file-upload-api.