i say this assuming you use Synthesizer V Studio Pro-
i think i would typically write that sound as "oooo" if its the same sound coming from "you", hopefully im understanding right. the simplest way to get figure out what real word you want a sound from while not knowing the program's phonemes would be to make a note and type in the word "you" and then edit out the consonant phoneme on the note, being 'y'. the phoneme you should be left with on the note is "uw". from there you can add notes with a "-" phoneme to stretch it.
this sound can easily be obtained by entering the lyric "oo" into a note, for future reference! but literally typing in a word that sounds similar can be helpful if you dont know what the phoneme might be.
In case you dont know how to edit the phonemes and not the word of a note- there should be some letters above your note after you enter words, double click that space. or click on the music note icon on the right panel, select your note- it is the note properties and you can also see a box that says "phonemes" where you can change it too.
i recommend experimenting with vowel phonemes to get other sounds if you're confused, combining some as well. as far as i am aware synthesizer v (studio pro, at least) doesnt have a phoneme chart to refer to in the program but on windows it can be found at this location on your pc C:\Program Files\Synthesizer V Studio Pro\clf-data . its not the best explanation for non-english speakers sadly but itll at least tell you all the phonemes.