RameshDada can you provide the URL and login details (admin) for the site ? Not here in this thread, but in the private discussion will be fine.
Also, you should never modify any files in the WordPress core as those changes will be overwritten in subsequent updates. Secondly, you risk further weakening the security of the installation if your changes allow existing functions that rely on other code you may have changed to execute in a manner that could render the system vulnerable. The advice here is that unless you are a security expert or have an excellent working knowledge and understanding of PHP, don’t make changes directly to the core - and especially, do not completely trust what you find on the internet and simply use copy and paste without first understanding the impact of the changes you are making.
Changes made via plugins is the preferred route, and even then, some plugins (as I’ve witnessed on numerous occasions) make the core vulnerable by changing the default behaviour.