You absolutely can read from channel 0 to channel 3 (1-4) in sequential order. Assuming you are using the AD7091R-4, you can simply program the channel register (ADDR = 0x01) with code 0x000F to enable channels 0 to 3 for conversion.
If you meant that you are using the 8 channel, AD7091R-8 and you want to convert channels VIn1 to Vin4 then simply write 0x001E to the Channel register.
More information on device configuration can be found in the datasheet
You absolutely can read from channel 0 to channel 3 (1-4) in sequential order. Assuming you are using the AD7091R-4, you can simply program the channel register (ADDR = 0x01) with code 0x000F to enable channels 0 to 3 for conversion.
If you meant that you are using the 8 channel, AD7091R-8 and you want to convert channels VIn1 to Vin4 then simply write 0x001E to the Channel register.
More information on device configuration can be found in the datasheet
