Hey,
I would like to remind that SD card cannot be used for Storage memory Expansion and you would have to stick with USB for the same
but, in any case if you want to use the SD card still to use as a storage drive . A detailed step by step instruction regarding the steps to follow while using the SD card in RUT955 is mentioned in the following link
https://wiki.teltonika-networks.com/view/RUT955_SD_Card
Please let me know if you face any issue during the steps
Thanks,