add a new sting

I need help. I use for this site the Icelock theme (child version) and I can’t translate some titles.
This titles i can set through the Custom theme page.
In the homepage.php file the code is:
<h2><?php echo get_theme_mod('icelock_title_recent_post_section', '') ?></h2>
I need to translate this string for 3 different H2.
Can I add new string? How?

Sorry for my english… 🙁

https://wordpress.org/plugins/polylang/