To open the Metadata Search app in the Salesforce lightning -
- Click on the App Launcher.
- Search for "Metadata Search"
- User should see the Metadata Search App, click on the same.
Metadata Search app is open. Now you can use this.
PS: View Metadata Search, Salesforce quick search app on Salesforce AppExchange: https://appexchange.salesforce.com/appxListingDetail?listingId=a0N30000009wgF7EAI