U.FL Connector selection?

According to the Datasheet we have a selectable U.FL Connector for an external Antenna on the nRF52840-MDK.
How can we select between the internal (Chip) an the external Antenna?
Do you have an code-example of the usage for the nRF-SDK 15.2?
I just need a BLE-Beacon every x ms over the external Antenna.

Thank you

Hi friend,
You can follow this step to use the U.FL connector: