I have faced the same situation when my DJI drone has fallen into the water. I have tried some basics steps at my own risk. 1) Turn the power off and remove the battery. 2) Check your warranty: If your drone is still covered by the warranty, there’s little more than you can do except put it in a dry, warm and ventilated place until you can send it off to your supplier or 'best drone repair shop for DJI Drones' 3) Towel dry the rest of the device. 4) Put the device in the oven at the lowest possible temperature, 125F to 175F, for several hours. This will dry any remaining moisture in the device. Do this as soon as possible. These temperatures are above the 104F that DJI recommends.

Recently I bought a '''DJI PHANTOM V PRO''' drone, and I facing the same problem with my newly purchased drone. Then I troubleshoot some basics instruction, now the issue has been solved. Now, It perfectly works. Anyway, your controller means remote controller, if you have still faced this problem you can reset your RC, or you can try this manual instruction: Open the Go app, with your controller connected and on. On the splash screen with the photo of the drone, hold down the little hamburger menu in the top left corner for at least 10 seconds. When you release it a firmware menu should pop up for the controller. Select the version number in the middle of the screen, scroll down the oldest version it will let you select save and refresh the firmware. When it's done restart your remote and follow the props to update it in the app.