Go to Setup → Settings → WhatsApp Setting from the sidebar and click on the Meta WhatsApp tab.

Enter the following, taken from your Meta for Developers → WhatsApp app:

• Access Token — the permanent (or system user) access token for your WhatsApp Business app. Required, masked after saving.
• Registered Phone Number — here this is your WhatsApp Phone Number ID from the Meta Cloud API (not the phone number itself), required.
• Language — the language code your approved message templates were created in, e.g. en_US. Required.

Set Status to Enabled and click Save. Enabling Meta here automatically disables the Twilio provider.