Tested on a CSG350-2LB 

How to check Mobile number and SIM Number so you would know which vni-0/10<X> to disable/enable the SIM

(Sometimes /dev/ttyUSB2 and /dev/ttyUSB5 interchange with vni-0/100 and vni-0/101 if you have dual LTE like CSG350-2LB. If only one LTE the default is /dev/ttyUSB2)

Open 2 ssh session to the Appliance. One will be for the screen and the other one for the cli 

sudo screen /dev/ttyUSB2 

AT+CNUM        ##Hit Enter and you will see the mobile number

AT+CCID          ##Hit Enter and you will see the SIM number

If Dual LTE like CSG350-2LB 

sudo screen /dev/ttyUSB5 

AT+CNUM        ##Hit Enter and you will see the mobile number.

AT+CCID        ##Hit Enter and you will see the SIM number.

Switching SIM slot 1 to 0  (To temporarily disable the SIM card)

sudo screen /dev/ttyUSBx (where X is 2 or 5)

at!uims=1     hit enter OK word will appear

at!uims=0    hit enter OK word will appear

Check if the SIM went back to SIM slot 0

AT!UIMS?    hit enter,  OK and 0 will appear

Only needed if it is not connecting automatically

At+cfun=1,1

On Appliance-cli:

adminBranch-cli> show interfaces wwan status carrier-brief           #To check if the status is already connected