Scrape it out, and reapply DAP kitchen and bath silicone of the color of your choice. There's endless tutorials and tips out there on YouTube and other platforms on how to actually do it.

Silicone will shrink as it dries, so make sure to squeeze it back into the gap. Another possibility for why it cracked was if they used grout instead of caulk. Grout is hard and shouldn't go against a wall, but there's mixed opinions on that, but grout on walls always cracks eventually.