• Sign in to your YouTube account and click on the gear icon in the top right corner to access your account settings.

• In the Overview tab, click on the Verify button.

• Follow the prompts to verify your account using your phone or email.

• Once your account is verified, you can follow these steps to upload a custom thumbnail to your videos:

• Go to the Video Manager and find the video you want to add a thumbnail to.

• Click on the Edit button.

• In the Overview tab, click on the Custom thumbnail button.

• Click on the Choose file button and select the image you want to use as your thumbnail.

• Click on the Save changes button.

Remember that your thumbnail image should be 1280 x 720 pixels and in a .JPG, .GIF, .BMP, or .PNG format. It's also a good idea to use an image that is visually appealing and represents the content of your video.