Here is what you should do in few steps:
1. Connect to your server using SFTP client (https://kinsta.com/knowledgebase/how-to-use-sftp/ here is the Kinsta host example, you may want to find instructions for your host)
2. Copy page.php from wp-content/themes/integral-pro to wp-content/themes/integral-pro-child/
3. Paste the code from this link to 27th line of code. https://pastebin.com/bW19c0jR
You may want to copy code directly from that source, as it doesn’t include any formatting.