On a phone that’s already using an eSIM, but not yet using a SIM card:
Insert the SIM card. Learn how to insert a SIM card.
When asked, "Use 2 SIMs?" tap Yes. Your phone will update.
After your phone updates, open your Settings app again.
Tap Network & internet and then Mobile network.
To set call and text preferences, tap your networks.
Tip: To have your phone ask your network preference every time, tap Ask me every time.

Change dual SIM preferences on your Google Pixel phone
You can choose which SIM your phone uses for data, calls, text messages, and more. Your phone uses that SIM automatically.

Set default SIM for data, calls, and text messages
Open your Settings app.
Tap Network & internet and then Mobile network and then your network.
For each network, set your preferences:
Data: Turn on Mobile data.
Important: Only one SIM can be the default for data. If you already have one set up, you'll get a notification.
Calls: Tap Call Preference. Then pick your default carriers, or tap Ask me every time.
Texts: Tap SMS Preference. Then pick your default carriers, or tap Ask me every time.