Generate random numbers on STM32L4

Hi to all,
I’m using an STM32L4R5ZIT6PU with the last mbed version 6.15.1; I’m trying to use on this mcu the hardware random generator following what I read to this link:

but I really don’t find how to enable FEATURE_EXPERIMENTAL_API and FEATURE_PSA features. Please, could anyone suggest me how to make it ?
Davide Urbano