Hi Victoria -
It's hard to know without seeing your presentation, but it sounds like you might need to edit your Voki character on each slide, and assign a an audio to it. Once you do that, and save your Voki, you should hear the audio you selected in each of the slides.
If this advise is not helpful, please post a link to your presentation and I will look into it.
Or, if you prefer, send it to firstname.lastname@example.org.
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