If you set the Webmaster Tool for the first time you need to follow the steps from How to set the Google Webmaster Tool.
If google says you need to verify your website again, follow these steps:
- Login to Webmaster Tool and select your website
- Go to the Google Settings menu
- Select the Verification Details
- Select the HTML tag and copy the Webmaster Code
- Go to your dashboard and add this code in Squirrly > Settings > Measure your Success