The kinds of repairs you do will depend a lot of the size, materials and purpose of the retaining wall. If it is just a decorative thing it will probably be pretty easy to do the repairs but if the retaining wall has an actual structural purpose it will probably be a little trickier.
Its good to have a long look at the retaining wall and how it is put together. Lots of people think that building a retaining wall is easy and they tackle the jobs themselves. You often end up with amateurish work that has more problems than it is revealing.