Hi @HiteshSingh,
The limit is relating to the xpack.reporting.csv.maxSizeBytes property in Kibana. I would recommend having a look at this thread and see if you need to increase the limit. I would advise caution though as setting it too high will impact the performance of your Elastic cluster.
Even then I wonder if you will struggle to get the full population out given you're looking to export millions of records. If you're not comfortable exporting in batches by specifying a time range, you could try having a look at the ODBC driver to access the data directly from Excel.
Let us know if either of those options work out for you.