The simple answer is no, not currently. (However, please read on...)
The aspect to bear in mind is that simply moving a run may not make sense. For example moving a 30 minute interval session from a Monday to a Tuesday could have significant impacts on your Wednesday run and the rest of your subsequent plan. Or it maybe that doing it on the Tuesday means that it can/should be increased from 30 to 40 minutes. Because of these complexities we do not presently have a feature to enable you to move workouts.
However, we do intend to build such functionality in the future. This will probably take the form of moving workouts with constraints and insights along with a preview of how your surrounding plan will change along with calculated benefits / detriments of the move.
Presently, of course, if you wish to run a future workout today, you can simply do so and let the system adjust your plan once it receives this activity.