Header font options not applying font variant (weight)

You forgot to add the font-weight option of the header in the dynamic_fonts.php
font-weight: <?php echo $ish_fonts[‘header_font’][‘variant’]; ?>;

I saw this while trying to overwrite the header and the headings font-family since I want to use a font that’s not available in your options (Roboto Slab, which you can find on google web fonts btw).
Is there a way to add extra fonts to the options of something or overwrite the dynamic_fonts.php in the Child Theme? Cause I wouldn’t want to edit the files in the original theme.