You don't need to reset your password because by logging in with your Google account you'll automatically be signed in. Since you originally chose to sign in with your Google account, you just sign into Google on that browser, click Sign in with Google (or click the G+) button and then you'll get signed in.

If you no longer have access to the Google account or Gmail address and want to use a different email, refer to I no longer wish to sign in with Google.

Here is a sample email:
---------- Forwarded message ----------
From: Blackbaud Authentication Services <>
Date: Fri, Apr 21, 2017 at 5:18 PM
Subject: Reset your Blackbaud account password
To: ""  

Your name,
We received a request to reset your password but noticed that this Blackbaud account uses Google to sign in. Rather than change your password, sign in with Google.
Didn't ask to change your password? Then just ignore this email.
Your friends at Blackbaud