Writing

So two years now that I have started using musescore...in my early starts, I have done something by inattention and now I realise that I need it. I do not know how to do it. If someone knows how to, please do tell me. My platform is windows 10 64 bit if that helps.
See the attached file.
See how on the quaver, one note is at the top and the other is at the bottom, kind of the two notes are inversed. I have done that but I do not remember.