HI Pat!
There is always the hard way altering the database contents.

But also an easier way in this case.

First of all do backup from your current situation. Either full adif backup from your log, or even better; copy of your ~/.config/cqrlog folder with all files and folders it has.
With your favorite file browser you must set "show hidden files and folders" as folder ".config" (dot)config is hidden otherwise.
With command line console:
cp -a ~/.config/cqrlog ~/.config/cqrlog_backup

We are going to use "Group edit" that has no "ooops, roll back" - feature.

Open "QSO list". Select "Filter/create" and if you can define with that what qsos you want to upload again. Perhaps with start and end date limiting.
When filter is created press OK and check that you see qsos you wanted in QSO list now.

Then select File/Group edit. Note that opening window says that edit is used to filtered qsos.
From "field" selector choose "eQSL sent", from "value" choose "N" and press "apply".
Then close with "Cancel"

That should do it. There has been bugs here so be sure you are running cqrlog version 2.5.2 that should be ok (until someone finds another bug from group edit).

Group edit is very powerful tool. If you made mistake then only way is to close cqrlog and copy ~/.config/cqrlog_backup backwards to be ~/.config/cqrlog (do not try copying to any direction when cqrlog is running), or create a new log and do full adif import (in case you did only full adif export as backup).