copying part of a tag into another tag

Can anyone tell me how to copy part of a tag in (comments) into the (bpm) tag !

e.g. currently in (comments) is

11A - 135.09

I want to copy the 135.09 part and place it into the (bpm) tag leaving 11A - 135.09 in the (commments) tag.

I WANT TO DO THIS TO ALL MY SONGS AT ONCE PLEEEESE.

PLEASE HELP !

This is possible via an action:

Action type: Guess values
Source format: %comment%
Guessing pattern: %dummy% - %bpm%