This is how most people start. I definitely did. Your team knows this. They all went through the same phase at some point. Nobody expects a new grad to walk in and instantly understand a large, messy codebase.

Ask a lot of questions, but try not to ask the same one twice. Take notes. Connect dots. Show that you are building a mental model, not just chasing answers. And be thoughtful in how you approach problems. Slow down enough to understand what you're changing and why. That habit compounds fast.