If playing around with phonetic spelling, punctuation, and different Overdub Voice Styles still does not produce a sufficient result, you can improve the quality of your Overdub Voice by re-training your voice with additional higher-quality training audio.
You can achieve higher-quality audio by recording in better recording conditions: in other words, using a higher-quality microphone and recording in a quieter space. To re-submit your training data, go to Overdub > Your Voice > ‘Open Training’ and record additional audio into the app. This will publish a replacement for your Overdub Voice.
Please keep in mind that you may only submit your training data once a month.