How do I move all dates 3 months later in a duplicate dashboard?

Hi,

I have a dashboard of a process with different steps. Each step has a starting day and an end day.
Now 3 month later I want to do again this process with the same steps, I duplicate the dashboards, but I would like to add 3 months to every starting day and end day. How can I do that?

I would appreciate very much for your help!