Hi Md,
That is unfortunate: as you've learned (the hard way), once an input custom parameter is dropped from a form, so too is the custom data that was contained, and even if you then re-add the input custom parameter, the data is not recovered.
If it just happened, I'd suggest you log into [yourdomain].preview.workfront.com, create a view that includes all such input custom parameters, and use it to export all of the information to Excel as a backup (before preview is then overwritten this weekend).
With that Excel file in hand, you can then either re-type the data manually into [yourdomain].my.workfront.com, or if it is warranted, use our Excel Updater solution to perform the updates on your behalf.
Good luck either way.
Regards,
Doug