Using the Prezi Desktop app, click the three dots (...) on the presentation thumbnail and select Download/Export → Offline Presentation . You can export as a .EXE for Windows or a .ZIP for Mac.
For users without a premium subscription, which is typically required for direct downloads, these workarounds provide a "better" path than simply hoping for stable Wi-Fi: How to download a Prezi presentation for offline viewing download prezi presentation from link better