Scuffed leather books are such a typical problem. Here is a one paragraph answer that is a summary of a lot of information. Be cautious and practice on a book that is not valuable.
You will want to apply klucel-g to (at least) the scuffed areas to consolidate them and make it safer to apply any coloring.
Next is Coloring. This is an advanced thing to do because it cannot be undone and can make it worse. Practice on an inconspicuous area.
You can match acrylic paints for color touch up or you can buy several high quality shoe creams like Tarrago or Sapphir (not polish!) and blend them to get an approximate color. Looks like you have two colors to match. Less is more. Only touch up the areas that are scuffed. Don’t cover the original coloring if you can help it. Overlap will cause a halo effect although shoe cream will be more forgiving than acrylics. You will need a TINY brush.
After the color is fully dry you can apply SC6000 to the scuffed areas and Hewit’s Leather Dressing to the undamaged areas.
I recommend taking this course on leather book care $14.99 https://saveyourbooks.com/course/4-101-caring-for-leather-books/ or at least take the free foundation courses on the site.
This one is on coloring leather: $0.99 https://saveyourbooks.com/course/8-book-repair-for-book-dealers-color-touch-up-for-leather-books/
I hope this helps!