It’s easy to move a workout/ride. Go into the workout itself you want to move. At the top of the page, tap on Move, then select the day you want to move it to. Generally you can’t move a ride to a day before or after your plan start/end dates.
If you skip a workout, it’s treated as a rest day. Down the road, we’re going to build out some cool functionality where your plan will automatically update based on your reason to skip a workout.
If you need a longer warm up than is planned for you, then it’s no problem. You can take some of the main workout time/efforts and add it into your warm up, thus reducing your main workout section. The key thing to remember is that you want to hit the total time for each zone that is planned. If you achieve this slightly differently from what is written, that is ok.