Add accidentals to trill text

Hi all, I'm trying to add an accidental to the trill articulation symbol, as seen on page 3 of the attached PDF. Dragging and dropping the accidental doesn't work, nor does double-clicking it while the trill symbol is highlighted. I've tried it both as an articulation and line (as suggested here: https://musescore.org/en/node/267596), but it didn't work for me. Any ideas? I've also attached the score I'm working with.