Please see the attached picture of a bar from my waltz. I just want the left hand chords to be quarter notes on beats two and three but no matter what I do it won’t convert, I just end up with this mess of 16ths, ties, and dots. 
Looks like an XML import, and/or you used Force Duration. Try Edit–Reset Appearance.
Strange. Reset appearance didn’t do anything. I found I had to convert the first chord to a half note, then quarter, then copy and paste it on the third beat. Thanks for your suggestion!
Oh, I didn’t look closely enough at the screenshot. It’s because you have notes of different durations there. Yep, it’s frustrating to work with tied notes of different durations. You could overwrite with a quarter note, or to untie the figure.