Maybe a funny question to ask here, but if there are any job openings at the library, where can I find this messages? Kind regards

Openings in the library are very often published in Kirjastot.fi, https://www.kirjastot.fi/ammattikalenteri The difficult part is that they are published in Finnish, but if you can read Finnish or translate the  messages, it's the easiest way to follow them. If you want jobs in Kouvola, you could follow Kouvola City jobs in their website, https://www.kouvola.fi/tyo-ja-yrittaminen/avoimet-tyopaikat/ also in Facebook, https://www.facebook.com/uusityokouvola . There are of course all vacancies, not only the library jobs.