Hi,
Please refer to the documentation in the SDK installation folder:
…NXP/S32DS.3.4/S32DS/software/S32SDK_S32K1XX_RTM_4.0.2/doc/Start_here.html
In the part Communication Driver Examples you can find FlexIO Uart…
...NXP/S32DS.3.4/S32DS/software/S32SDK_S32K1XX_RTM_4.0.2/doc/html_S32K144/flexio_uart_s32k144_group.html
Best regards,
Ladislav