If you’re just editing a post or page’s content, or have a block theme and want to make more of a site-wide change, just add the Social Icons block: https://www.ads-software.com/documentation/article/social-icons/
If you don’t have a block theme, you’ll need to consult with your theme’s support for available options.
1 other note though, there is no “free plan” here, WordPress is free software, developed and supported entirely by volunteers, and backed by donations to a non-profit foundation.
If you really do have a “free plan,” maybe you’re referring to WordPress.com. In which case, we can’t help with that here.
To clear up any confusion, WordPress.com and www.ads-software.com are two different entities: https://www.ads-software.com/support/article/wordpress-vs-wordpress-com/
WordPress.com has complete documentation and support contacts at https://wordpress.com/support/