I have used this template on several pages and I have always found the option to add a search button, with a magnifying glass icon, in the header builder.
This time I can’t find it.
You can see it https://share.zight.com/WnuWpzo0
Please deactivate all the 3rd party plugins and activate only theme-required plugins on the site and then check the issue. I am sure your issue will be solved. Then Activate the 3rd party plugins one by one and check which plugin is creating the issue for you.
Otherwise, if the issue still exists then keep the 3rd party plugins deactivated and let me know I will further check on your site and give you a possible solution.
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