How to write a trill or 3 notes in one beat in 3/4 time

I am trying to recreate the tune ST COLUMBA which is written in 3/4 time and has one measure which contains a half note and then a trill or 3 notes connected with an arch and the number 3 written over it to indicate you sing those three notes in the last beat of the measure. I can't figure out how to create that in the muse score software. Sorry for the uneducated language or confusing explanation. Any help is appreciated!