Because this is a state actor, you can't just send the police after them: they have fighter jets (and it was a fighter jet that grounded the plane). You have to ask whether you're willing to go to war, or impose collective punishment on the people of Belarus via something like sanctions. The EU has already taken diplomatic steps for previous offenses like barring Lukashenko personally from the EU, and the US has banned loans to the Belarussian government in the past as well — and those bans remain in place today.
There are probably more diplomatic levers to pull, but TBH none of the existing ones have seemed to do anything. States are okay at enforcing laws within their borders without massive death or total economic destruction, but don't seem to be very effective at enforcing much inside of someone else's borders barring those options.