You can easily find the block to do exactly this. You can configure the captcha solver you want to use in RuriLib settings, then simply add a solve captcha block to the config and an if statement so it will only solve the captcha if needed.
IF STRINGKEY @data.SOURCE Contains "Captcha required"
Here put SolveRecaptchaV2 block and as output variable put something like SOLUTION
Then make a POST request to the site and pass the <SOLUTION> in the post data alongside other data
ELSE
Same request without the recaptcha stuff
END