With the airplan
The closest airport is Bardufoss. You can reach Bardufoss via Oslo. To Oslo there are several airlines to choose from, f.e. Norwegian and SAS. From Oslo to Bardufoss is SAS the only airline that offers flights. We pick you up at Bardufoss airport.
Norwegian also offers flights from London directly to Tromsø where you can take a bus to Setermoen. The bus ride lasts about 3 hours. We pick you up in Setermoen.
Information about the bus transfer: https://en-tur.no/
It is best to book with SAS directly on their web site: https://www.flysas.com/en