Step 1: Sign in to PowerApps Portal and Select the Environment
Sign-in to PowerApps Portal and make sure you select the Environment where your application resides.
Step 2: Select the App You Want to Embed and Go to the Details Page
From the Apps list in your PowerApps Portal, click Details on your PowerApps application and copy the App ID.
Step 3: Set the PowerApps ID in Your Page Builder Element
Paste the copied ID into the PowerApps ID field from the Settings tab.