Delay several tasks at the same time


I am wondering if there is any way to delay several task at the same time or even the entire project. For example, you have a construction project and your whole project is delayed 2 weeks because you don’t have the permit to start your works.

Is there any easy way to do it? So far, the only option that I’ve seen is changing the tasks manually, which would take ages if you are having hundreds of tasks… I have tried exporting to Excel and importing it, but it is limited too (I will create a different topic for import/export indeed).