Hi oskarst1606,
You can play with the settings of Voice presets to get different results. For example, in Female-2 voice, try to change pitch % of Voice Pitch Shifter which can make your voice more softer. But if you want to sound exactly like a teenage girl, in terms of Audio Processing, that is currently too difficult to achieve, as every teenage girl has different voice characteristics, pitch, frequency, tone etc.
Regards,
Yusuf