The only built-in way to export worlds in bedrock edition is with Minecraft for Windows 10. If you have a world on another device, you can to transfer it to Minecraft for Windows 10 via Minecraft realms. Once you have the world on Windows 10 edition follow the steps below to export;
- Open Minecraft for Windows 10 and click “Play”
- Find the world you want to export and click the pencil icon next to it
- Scroll to the bottom of the page and click “Export World”
- Chose where you’d like to save the world and click “Export”
- Minecraft will let you know when the export is finished.
- Your world has now been exported to the location you chose earlier.
That’s it! You can double click the created file and it will be imported into Minecraft.
If you need any more help with this, or other Minecraft questions, make a post on r/MinecraftHelp where one of us will be happy to help.