You can set up MultiSIM in the Apple Watch app on your iPhone. Before you start, make sure your smartphone and Apple Watch are connected to the mobile internet and not via Wi-Fi and that they aren't part of an existing Familyconfiguration.
- Open the Apple Watch app.
- Tap on the «My Watch» tab, then tap «Cellular».
- Select «Set Up Cellular».
- Follow the instructions to finalise the MultiSIM contract.
- You’ll receive a confirmation SMS as soon as MultiSIM has been activated.