MAGPIO pins can be configured with the Nordic-proprietary %XMAGPIO AT command.
For information on the %XMAGPIO AT command options, see MAGPIO configuration %XMAGPIO in nRF91x1 Cellular AT Commands Reference Guide.
For an example of a device using MAGPIO pins for LTE antenna tuning, see Nordic Thingy:91 X product page. For Nordic Thingy:91 X™'s hardware files, see Hardware files.