ICM-20948 watermark threshold

Hi all!
I use eMD-SmartMotion-ICM20948-1.1.0-MP SDK to bring up the IMU under low-level.
I can't get the info in docs and SDK about setting the Watermark threshold. Interrupts were enabled succesfully at all.
In the function dmp_icm20948_set_FIFO_watermark(s,800) the string

inv_icm20948_write_mems(s, FIFO_WATERMARK, 2, inv_icm20948_convert_int16_to_big8(fifo_wm,big8))

somehow allows to set threshold but is inconsistant absolutely, because FIFO_WATERMARK is put like register number instead real register number.

Watermark so useful feature for my project. Please, give an advice how to set watermark threshold correclty via register.

Thanks!