Populate tags from filename

I can't work out how to replace a tag in multiple files with a value (the same for each file) which I include in the action.
I have tried using a regular expression in quick action
Action: replace with regular expression
Field: %album%
RegEx: .*
Replace with: Hello Dolly
However if comes up with Hello DollyHello Dolly every time.
Can someone please help me to get it right?

If you want to get a string constant into a field, proceed as follows
load the files
select the files
either use the tag panel, the extended tags dialogue to enter the string manually
use an action of the type "Format value" for the field (here probably ALBUM) and enter as
Format string: Hello Dolly

BTW: what does your attempt have to do with the filename? I can't see a reference to the filename anywhere.
To get data from a filename, use the function Convert>Filename-Tag