The resolution of this issue, which has been completely fabricated by Trump, is to push for defining the problem (which seems to change every day).
There has to be a political campaign ran by Denmark and it’s NATO allies combined with a communications one, that pushes the US to be clear as to what their national security issue with Greenland really is.
Then, you go all out in diplomacy in the US (meaning in Congress and the news outlets in an organized fashion) to remind that there is already an agreement in place with the US to give them all access they feel is necessary for those DEFENCE needs.
The idea here is to demonstrate to the open public in the US, and in Congress in particular, that there is no real “national security” issue here, but just an attempt at seizing the natural resources of a friendly, allied country.
Expose the lie and the issue goes away, IMHO.