But when I check the source code then it shows different ALT tag that I have inserted in the media library.
It looks like my website automatically fetches ALT from the image title.
Any of you please suggests me the solution? Do I need to change in the theme file? If yes then what it would be?
]]>You could try going in the Customizer and preview a different theme to see if the alt tags are changed by the theme.
If not, I would try installing Health Check plugin which has a troubleshooting mode that allows you to disable plugins for the admin only so you can isolate the problem.
Once you find the culprit, please ask the author to fix the problem.
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