Hey Muthu,
The reviews section is not the best place for support. Can you please open a new support ticket at https://www.ads-software.com/support/plugin/wp-old-post-date-remover so that I can help you out there?
In that ticket, can you answer this:
1. Are you running any caching plugins or other caching system?
2. Have you configured my plugin on the settings page to remove the dates after a certain period?
Thanks!