Please follow the following steps to fix your issue:
Go to Dashboard => Appearance => Customize => Site Identity => And you can see below text at last of left side => keep the icons => Then save it.
Site Icon
The Site Icon is used as a browser and app icon for your site. Icons must be square, and at least 512px wide and tall.
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We hope this will be helpful to you if not then please let us know, we are happy to provide solution asap.
Hello
I am sending you a picture of my WP Left site bar, there is no Site Icon menu, this is my problem. I made the same theme for a friend and in his WP this site icon exist in my Wp press does not. 🙂 Please help. I can give you my password so you can log in to see if you can fix it.