There are some simple steps you have to follow to set custom YouTube thumbnail. Your account must be verified for that If your account is not verified then don't take tension just click here . Then you have to select your Gmail account and you have to give your contact number. Then Google will send you a OTP on that number and you have to click on submit after typing OTP. Than your account will be verified. Now Steps:- 1. Open YouTube Studio app. 2. Click on menu ,then videos. 3. You have to tap on edit . 4. Now tap on edit thumbnail. 5. Select thumbnail:- •If you want to add a custom YouTube thumbnail then tap on custom thumbnail. •Or you can select one of three auto-generated thumbnail. 6. Now it's time to confirm your thumbnail tap on select. 7. Finally,tap on save. Thanks for reading.....