Business Process: Extract part of email subject to use as parameter to assign proper category

Hello Creatio friends,

I've set up an email box to generate cases, but it is not assigning category/sub-category. 

I'm working on a business process to re-assign email generated cases to the proper Cat/sub-cat. I want to pull the first word after [EXTERNAL] from the email to use as a match to proper Category. Sub-category can be a static lookup value for this use-case. 

For example with a subject line of "[EXTERNAL]Chicago - Assistance needed" I want to just extract Chicago, then use a BP to do a Modify Values:  Category = extracted text.

Any great way to go about this?

Thanks,

--Israel