Cousins using my youtube account?

During the summer, I logged into my own youtube account on my polish grandmother's computer to watch videos. My younger cousins also share that computer, which like to watch Minecraft videos, gaming, etc.
FFW a few months later, in my search bar, there have been recent searches that I didn't do. I guess I forgot to log out of that account there. I'm pretty sure they are my cousins (they are typed in polish, and they are gaming videos). I also have new subscriptions to channels which I didn't subscribe to. Does anyone know how I can log off my account on that computer, or message them to log off? It's my account, so I can't exactly message them lol.