You can exchange up to 10,000 hryvnia once at the bank where you hold an account. The exchange can also be made in several instalments. Generally, this currency exchange is free. When exchanging currencies, you must show a valid identity document.
Alternatively, you can exchange money at the Reisebank in Leipzig central station. However, there are fees for doing so.
https://www.reisebank.de/die-reisebank/magazin/umtausch-von-hrywnja-griwna