We tried moving FP+ up on our trip last October at EPCOT and it was a disaster. Be very very careful if you are trying to do this from the
MDE app. We found that out the hard way. We were hoping to get through our 3 quickly and maybe get a 4th for a TT. We rode Soarin with our FP+ then I got on MDE and attempted to move Nemo up. The app showed an earlier time as being available and was being assigned to the 3 of us. When I hit confirm it moved our FP+ to 6 HOURS LATER instead of the time it showed it was giving us. When I quickly tried to move it back, it showed me our original time was not available, so I marched myself over to a kiosk for help. They told me it was either an MDE glitch or someone else was trying to book it at the same time and just happened to hit confirm before I did. They could not fix it for me. All they could do was either set my FP+ to Captain EO almost immediately to let the hour burn quickly, or to get me a FP+ for Nemo that kicked in 2 hours AFTER our original FP+ that I had been trying to move earlier. You are safer going to a kiosk than using the app.
Also, another thing we found out the hard way is that you do NOT want to change attractions for a FP+ on MDE unless they have fixed the issues with that since our trip. If you are trying to change attractions on the app- it will appear that the attraction is available for your FP+ time, but it really probably isn't. What it is actually doing is showing you all the attractions where FP+ is available for the rest of the day. Then, when you hit confirm, it assigns you the first available time for the attraction you are switching to. So, for example say you have a 10:00 a.m. Splash Mountain FP+, but decide you would rather have something else. When you click to switch attractions, it might show you 7DMT is available and it will look like it will be switching it for the same time 10:00 a.m. FP+; however, when you hit confirm, you might find you have an 11:30 p.m. FP+ if that is the first and only time of day one is available. If you go to a kiosk, they can tell you exactly what is available when so you do not have any unpleasant surprises like we did.
You are talking about trying to move Soarin up. I would be particularly careful with that one on the app, as it is one of the 2 FP+ in the highest demand. It is hard to get Soarin or TT the day of, and if you mess with it and the app glitches, then you could totally lose it and be out of luck on Soarin.
We had other EPCOT days, and we tried to do either Soarin or TT FP+ when the park opened and then get things moved up as fast as possible to try to get a 4th for either Soarin or TT. We have never been able to pick up Soarin or TT as a 4th. We are not there in high crowd times either.