Before using DXKeeper, I had entered a bunch of QSOs into the QRZ logbook.  Recently I exported them from QRZ to an ADIF file and imported it into DXKeeper. 
Each of those entries now has an "N" in the LOTW Sent field, so it can't be added to the QSL queue for upload to LOTW. 
I don't see any way to manually update the field to 'R'.
Is there any way to batch process the correction?

--

73,
Neil W0NRP

Before using DXKeeper, I had entered a bunch of QSOs into the QRZ logbook.  Recently I exported them from QRZ to an ADIF file and imported it into DXKeeper. 
Each of those entries now has an "N" in the LOTW Sent field, so it can't be added to the QSL queue for upload to LOTW. 

+ Presumable that's because each of the ADIF records you imported contains the field <LOTW_QSL_SENT:1>N  

+ As you can see in the ADIF specification, that means "do not upload the QSO to the online service":

http://adif.org.uk/ADIF_Current#QSLSent_Enumeration

I don't see any way to manually update the field to 'U'.
Is there any way to batch process the correction?

+ Yes:

1. Filter the Log Page Display to contain the QSOs whose "LoTW Sent" items you wish to modify; see

https://www.dxlabsuite.com/dxlabwiki/QSOFiltering

2. Use the "Modify QSOs" panel on the "Advanced Sorts, Filters, and Modifiers" window to modify each Log Page Display QSO's "LoTW Sent" item en masse; see

https://www.dxlabsuite.com/dxlabwiki/QSOModifying

+ Don't skip step1!

+ Note that the name of the field to modify is

APP_DXKEEPER_LOTW_QSL_SENT 

    73,

         Dave, AA6YQ