reCaptcha & https, altering through which .php page?

Dear all,

From https://developers.google.com/recaptcha/docs/tips?hl=nl I understand “In order to avoid getting browser warnings when you use reCAPTCHA on an SSL site, you should replace http://www.google.com/recaptcha/api with https://www.google.com/recaptcha/api when you request a challenge. Your request to reCAPTCHA would look like this:”

That is clear. However, unfortunately I have not been able to find on which .php page in editor this can be altered.
Can you help?

Thank so much in advance.

https://ww.wp.xz.cn/plugins/google-captcha/