Hello,
This command must be entered via CLI. To do so, you can either download an SSH client, such as PuTTy, and login to the router using SSH or you can access router's WebUI, by going to System -> CLI. For username enter root, for password, use router's WebUI login password. The full command, which has to be entered, should look like this:
gsmctl -A 'AT+CGDCONT=1,"IP","staticip"'
Best regards,
Žygimantas