When you search for a cache there are times when you do not find it. GSAK will automatically update this status from your geocaching.com GPX file. However, there are times when you may want to do this manually yourself.
You can manually log your DNF in GSAK 2 ways.
Solution 1: by checking the DNF check box in the grid. (if this column is not showing you can add it to you display view via Tools=>Options=>Display)
When you check this box, GSAK automatically enters the current date as the DNF date (You can also add this column to your grid view)
If you do not want the current date for your DNF, then double mouse click this check box. When you double click this check box the behaviour is:
1. Sets the "DNF" check box
2. Sets the DNF date to the current date
3. Opens up the standard GSAK edit dialog already focused on the "DNF Date" date with the calendar showing ready for selection
Solution 2: The other way to set the DNF flag is to just right mouse click on the cache, and select edit... You can then set the DNF flag and the DNF date.