Thank you so much for using our theme Grip.
Actually, there is no such option available in the theme to use your own custom link for the logo. However, you can customize the theme. Inside the theme file, you can find the header hooks file, candidthemes/functions/header/hook-header-main.php file and in place of the custom logo, you need to write the code for the logo and the link.
If you are familiar with the codes, you can do it yourself, otherwise, we recommend you to hire the developer. But, if you purchase the premium version, we can help you to customize the code to your main site link.