Log into the WordPress dashboard and click Appearance > Theme Options. Please select Twitter widget settings and add required API keys. You can get those API keys on https://dev.twitter.com/apps.
Log into https://dev.twitter.com/apps using your twitter access credentials
Click on “Create a new application” and fill all the required details
You are not done yet, please click on “Create my access token” to get the rest of API keys
Now you should see all your API keys that is required for your twitter widget. See screenshot below.