For assignments you can bulk edit the due dates at one time on the assignments page.
https://youtu.be/DOCgbEXV1J4
On the calendar you can drag and drop events, assignments, to do, and appointments from one day to the next, but it isn't possible to select multiple items, so a bulk move wouldn't be possible.
Not entirely related, but I'll share a trick that not everyone knows about. In the mini calendar to the upper right corner, you can change that to a different month. If you want to move an item from one month to another month, select the destination month in the upper right and drag and drop the event from the big calendar to the mini calendar.