I am not sure that the license gets added to Splunk at all...(Splunk licenses are xml)
Splunkbase notes that the tripwire apps are "Hosted Externally" and points you to tripwire for the download.
I would check for support or install instructions from Tripwire. Perhaps their customer portal? My google-fu has not returned any info on install steps beyond whats on splunkbase, and that makes no mention of license.
All I could find was this EULA making pretty clear Tripwire is on the hook for anything to do with the app, and the instructions on the splunkbase page: