Hi
So two parts,
Now that you have specified apply to oldest any new payments will be automatically applied but you have some that are still open from before you enabled that setting
There is no process that you can run in NAV that will go and close those automatically, ether they will have to be done manually, or you will need to get a developer to write something specific to do it for you
Generally it is not a problem adding fields to a report if NAV has the relationships and can therefore find the information however it is not something that can be done by a non devloper, you would need to get your NAV partner involved to modify the report
Cheers
Nev