Adding guitar chords on an eighth beat

I'm try to score guitar chords and lyrics for a 4/4 rhythm song.
The staff is tabs and then I use the 'Fill with slashes' tool. I click on a slash and add Chords and lyrics - so far so good.

But, there are some tricky rhythm parts where the chords change on the upstroke / eighth beat. How can I convert from 4 down beat slashes in a measure to eighth note slashes so I can indicate that a chord change is on (for example) the "one and"?

When I select one of the slashes and click an eighth note in the note input bar, it adds an eighth rest after it and there seems to be no way that I have found to cover the rest back to a slash.

Is there some basic concept I'm missing here?