First, navigate to the campaign where you'd like to connect the Google Search Console integration, then click "Integrations" from the menu on the left side of the screen.

Next, either search Google Search Console in the upper right search box, or click the SEO category, then click Google Search Console.

Then click Connect Account.

A window will pop up asking you to enter your user name and password for your Google Search Console account. Enter the user name and password of the account that has permissions to the GSC client account which you would like to connect.

Next, you will see a screen which says "Application Connection would like have offline access". Click "Allow".

Finally, you will be prompted to select the customer account which you would like to connect. Click the radio button next to the appropriate account, then click "Save".

If the account that you would like to connect is under a different GSC account, and you need to enter different credentials to access that account, click the button that says "+ Connect New Account", then enter the appropriate credentials, and step through these screens again.