I have two lines on my device with dual SIM - how do I change the line before calling?

Switching which line to call from

iPhone:

1. Open the Phone App
2. Select Contact to call or dial the Phone Number
3. Tap the Default Line near the top of the screen
4. Select which line you would like to use for calling

Android:

1. Go to Settings > Connections > SIM card manager
2. Select the Preferred SIM card for "Calls"