On any Fundraising Page raising funds for a charity that is registered with Good2Give, the 'Donate from your Pay' button will appear as a Payment Method.
Click the button, login to your Good2Give account when prompted, and complete your donation on the Good2Give donation screen.
For a detailed how to guide see How to Donate through Workplace Giving https://support.gofundraise.com/hc/en-us/articles/115016022628-