Hello,
You can use DRDYBCase3 shown on page 40 of the datasheet. When DRDYB is asserted issue a read command using controlled streaming as shown on page 47. Read registers 0x19 to 0x1C. Register 0x19 bits 2:0 show the channel number that is in the ADC data being read. The DRDYB signal will be asserted every time new data is available in the ADC registers.
The code application note (snaa134) on the LMP90100 web page has some good information and code for reading the data from the ADC registers.
Mike