[karussell]

You could introduce (or write more) tests from your side for new feature that you write or for bugs that appear. But in general it takes a bit more experience to get unit testing into existing code, but not undoable and you could practise this for a smaller, independent or even hobby project. Still, the critical part is to get support, not just acceptance, from your boss as sometimes "less problems later" argument does not convince them as "it always worked well without tests".

And just adding tests isn't the only thing it takes to improve the software quality.