SoapUI testing: remove quotation marks from session ID

So, I am new to SoapUI, and working with API's in general, but I am trying to set up an automated test for a REST API in SoapUI (the freeware version).

The first call I make returns a session ID in JSON, which is placed between quotation markslike: "session ID goes here". This key is needed, without quotation marks, in the next API call. I use SOAPUI's "Property Transfer Teststep", and this is working well, apart from the quotationmarks which are still around the session ID, resulting in an error responce by the subsequent call.

Any idea how I can remove the quotation marks? Ive been reading up/Googling on Xpath and JSONPath, which are some of the coding languages I can use in the screen, but I cant see how to use this to remove said quotation marks. Your help would be greatly appreciated!!