Can't seem to change a IV chord to a Dominant 7
dominant seventh IV is not diatonic. However, you can get the dominant seventh quality by borrowing from the dorian mode. Make a IV chord, select it, and click the borrow drop down menu and select dorian.
I know its not diatonic and I tried the dorian but the voicing is not the same. The whole system doesn't allow for easy access to very many standard blues options, 7ths and instrument mixing.