You can simple modify the expression, in laymans terms:
- (?<=TRN) defines a lookbehind
- (?=-) defines a lookahead
meaning we are telling our code to look in between.
- which will get the value from your screenshot.
For further reference, I can recommend @Steven_McKeering awesome post here, Regex help tutorial MEGAPOST – Making your first Regex post, Reusable Regex Patterns, Regex Troubleshooting, Sample Workflow and more