Adding Quarter Notes Underneath Half Notes

Not really sure if I am posting in the right place, but I wasn't sure where else to go...

I am using the musescore notation software to create some piano music. I don't really know how to describe my issue but I will give it a go anyway!

Basically on one bar in the bass clef, I have 2 chords, which are both half notes. However, I also want 4 quarter notes to go underneath them on the same bar, but I just cannot figure out how to do this? Whenever I try to do it, it just adds another note to the half note chords. Can anybody help (please?!?)

Thanks