If lower, hum your lower notes and emphasize "O" and "U" if you sing. If you're going higher, "E" and "I" are more prominent. You can also just raise the tone of your voice a few notes when you talk, or lower a few notes. I sing a full scale from the lowest note I can hit to the highest when I shower and then sing songs in both ranges, since I prefer to have a wide range (I'm genderfluid). Try singing with the previous tips and see if it makes a difference. If not, I'll think of more ideas! :3