I dont find an option to upload favicon in website settings of erpnext15.
Thank you very much, I was checking in home section only.
This is good for basic 16x16 favicon. Some have the opinion though that one favicon is not enough these days. See here. If you want to get fancy and add other favicons optimized for different browsers/devices, you can add some of these lines to Website Settings, Header, Robots:
<link rel="icon" href="/files/favicon.ico" sizes="any">
<link rel="icon" href="/files/icon.svg" type="image/svg+xml">
<link rel="apple-touch-icon" sizes="180x180" href="/files/apple-touch-icon.png">
<link rel="manifest" href="/files/manifest.webmanifest">
Then, attach those to the website settings document so they can be served.