JavaScript TextField Help

I'm completely new to JavaScript (please bare with me) and I need to edit the value in a text field.

Here is the value I initially populate the textfield with: OperationBO:TEST,ASSEMBLE-1-CM,#

This is what I would like to end up with on the exit: ASSEMBLE-1-CM

Here is the path to the textfield: PrintContent.#pageSet[0].Page1.Header.BandR.#subform[1].Router.Row1.Operation::exit - (JavaScript, both)

Really appreciate any help that can be provided.