Hi @IniobongNkanga-8038 ,
Thank you for posting in this community.
I tried testing with your method, and everything worked fine. But don't worry, there are other ways we can modify your SITE LOGO THUMBNAIL.
1.Prepare the image you want to replace and change the name to siteIcon.png (the image type should be png).
2.Navigate to the "Site Assets" library. Upload an image and replace the original one.
3.Clear browser cache then restart it.
Please try to see if this method is useful.
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