1. To use multi-measure rests, you must have more than one instrument in your score.
2. First go to Score>Dynamic Parts and choose a part to extract.
3. Next, go to Score>Part Options and choose "More."
4. Finally, choose a value for multi-measure rests. If you choose the number 2, this means that anything that is exceeding 2 measures of rest will be converted to a multi-measure rest.