Unable to access external sd card

I have loaded the firmware through eMMC flash,
now i want to access the external sd card which is empty.
I want to mount the sd card to mnt so that i can access it, and also i have tried command lsblk to check if there is any external sd card connected but failed.

How to enable port to access external sd card, and how to mount it.

Help on this is highly appreciated. thanks.

Hi, which carrier board do you use for CM3 and which os you used.

I am using waveshare board
https://www.waveshare.com/cm4-to-pi4-adapter.htm

and burining the cm3 radxa image took from git.

from this link i am using
radxa-cm3-io_debian_bullseye_cli_b25.img.xz