Hi Shubham,
You can migrate your data if required or query it directly from its current source.
There are some Modules that help you achieve that and can be easily downloaded from the Market Place.
In your case you might need the ‘DB Connector Module’ to query or ‘Replication module ‘ to transfer the data from current DB to the new Mendix app DB.
‘Excel importer Module’ will easily help you insert your data from Excel sheets into the desired tables based on the sheet used.
Thanks,
Sufian.