Hi @Kim Ryan ,
The logo you said is Hub site navigation logo. It will be upper left corner after it associated with sites.
If there is not a Hub site navigation logo, you can click Settings in hub site. Choose Hub site settings and you can see the panel like this:
Then you can upload or change the navigation logo. For more information, please refer to: https://support.microsoft.com/en-us/office/set-up-your-sharepoint-hub-site-e2daed64-658c-4462-aeaf-7d1a92eba098
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