Hi John (BOF)
I've used HamRS because I didn't take my computer to the park. I wrote the QSOs on a piece of paper and for typing them HamRS is easier than Log4OM.
Here are instructions for Log4OM that you are missing. It seems that you already figured out how to export the ADIF.
Where the info goes in Log4OM?
Take a look below:
This is a real example from my activation on Saturday for P2P - Note the "Comment" field I wrote "p2p":
Contact's details - Note the "Sig Info" field - You write there the OTHER person park reference:
In "My QTH" you have the fields that you need to enter for YOUR park - Field "My Sig" = POTA and field "My Sig Info"=VE-5093 (your park)

That's all really.
Now you don't need to enter all this information one by one in Log4OM - You can use the bulk edit option.
From the Menu select Utilities -> QSO Manager
Select all contacts that you made at the park and click button "Single field update" (example below)
Select Field to update and set to MySig enter POTA en value and click on Update button. All the previously selected QSOs will have that value now.
Select Field to update and set to MySigInfo and enter your park reference and click on Update button. All the previously selected QSOs will have that value now.
Hope that helps.
73,
Pablo, VA3HDL