We can find duplicate record by using 'POST' builin in when_new item instance trigger at item level in detail block.

POST;

Writes data in the form to the database but does not perform a database commit. It's temporary commit thats useful for duplicate validation.

Create a trigger at form level When-database-trigger Post; (this
command will temporary apply the changes to the database) Than you find by Sql
Query if it is duplicate Record.