Are you referring to the photo of the Office 365 groups similar as below?
If so, you can change it by following steps below:
Office 365 Portal.
2.Go to Mail> Find the Group under Groups> Click the picture> Click Change photo icon as below.
3 people were helped by this reply
Did this solve your problem?
Sorry this didn't help.
Great! Thanks for marking this as the answer.
How satisfied are you with this reply?
Thanks for your feedback, it helps us improve the site.
How satisfied are you with this response?
Thanks for your feedback.