After that open admin > contact form > integration section
Go into Google reCaptcha website into new tab . Login into it . Enter the lable and domain name . After that submit the form. Google will give you Site Key and Secret Key . Copy these two values
Got to other Integration section and enter these two values and save the form.
Navigate to the Contact Form 7 form where you want to add the Captcha protection. Edit your form and Enter the [recaptcha] code