Like everywhere in the world, there guidelines to follow for international visitors when planning a trip to the Nordic region. You can find below some links to official pages which should provide the necessary up-to-date information you need to know.
The Official Finnish Border Control – this is the official Finnish Border Control’s pages
Visit Finland – information from Finland’s national tourist office, and can be much clearer to understand
Norwegian Institute of Public Health
Visit Sweden – information from Sweden’s national tourist office