If you go through our documentation then, you will find all the information you need there. For example, here https://www.wikitude.com/external/doc/documentation/latest/androidnative/triallicense.html#where-should-i-enter-the-license-key it describes how to insert your license key.
I'm having the same issue. I have a trial License key but I'm not sure what to do with it. I think my biggest issue is I don't know what the WTWikitudeNativeSDK.h is. Is it a file?