Well if you mean your vehicle does not have a spring tensioner then you need to move out /adjust the tension by repositioning one of the components such as the alternator or the compressor in order to get the belt tight. Basically just unloosen(do not remove the bolt or nut just loosen enough to move the component) the component and using a breaker bar or a small pry bar put a little tension on the belt by prying out on the component and tightening the loose bolt or nut holding the component. This should get the belt tight enough for your purpose.
