1. Open the InDTU Configuration Tool and log in. 2. Go to [Configurations > All Configurations > Dial Parameters Setting]. 3. Enable "Dual SIM mode" and "Switch card without connecting the center". 4. Set "Application center link mode" to TCP (required for SIM switch). 5. Save configurations and restart the device— it will switch to SIM2 if SIM1 fails to connect to the center.