Enter the diary preview view:
Tap the export button in the upper right corner
Choose the export format (Text, Markdown, PDF, Image)
In preview view, tap "Export" to save your file
You can also export a diary by: go to Timeline page, swipe left one entry, and then tap the "···" icon
Bulk export: "Me"-"Data"-"Export".
Learn more about how to bulk export your diaries.