bulk tag field replace

i have close to 500 folders with one album in each folder

now, i want to bulk edit the mp3 tags, so that the %albumartist% field of each and every file is equal to the the %album% field

i have been trying to formulate an action, but i am not getting anywhere.

Can please some body advise me what is the most efficient way of changing the albumartist field of every single mp3 file i have to be same as the album field of that same file

many thanks for your kind assistance, and merry xmas

its in the FAQ's! But seeing as its christmas n all.

format action:
value: %album%