Editing grouped-note durations quickly?

Please see attached pics. I can’t seem to intuitively create an eighth-note triplet from a group of 16th notes. If I try to expand the 16th note durations to 8th notes BEFORE tapping the triplet mark, for some reason the second note goes missing. If I try making the 16ths into a triplet FIRST and then lengthening the durations, it messes up even more. Suggestions?
Screen Shot 2021-02-06 at 2.17.49 PM
Screen Shot 2021-02-06 at 2.18.33 PM

Screen Shot 2021-02-06 at 2.19.36 PM

Before pressing 5 to make them into 8th notes, turn on Insert mode (I). Then convert them to a tuplet.

SWEET! Thanks for the tip!