Once you have set the domain name for your Salesforce Lightning component, you can add the Config button.
More information here to add the domain name for your Salesforce Org,
Once you have added the domain name, follow the instructions below to add Config button
- Log in to Salesforce as Admin User of your Org
- Click the Setup button
- Click on the Object Manager Tab
- Click on the V4S App Tab
- Click the Page Layouts Tab from the Menu
- Click Edit for App Key Layout
- Select Config button from Mobile & Lightning Action and add it to the "Salesforce Mobile & Lightning Experience Actions" section
- Save the page
Now the Config button is shown in the V4S Mobile apps screen.