How to bulk move tag data to another tag?

Okay on a couple of occasions I have messed up on my tag data and this is usually for classical CDs. For example I import the Composer information into the Artist tag, whereas I actually want the performer in the Artist tag.

Is it possible to re-map or move on mass the data from say the Artist field to the Composer field?

Many thanks,

Paul

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This is an example how to add something to an existing field. You must just change "Field" and "Format string" to your needs, like
Field: COMPOSER
Format string: %artist%

Thanks Dano