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Click Sign In. This blue button is located in the very top, right corner of the screen. Click on the box the reads "Enter your email" and type your Google email address. Click Next. Click on the box the reads "Password" and type the password for your Google account. Click Sign In. You can access this person's channel in two ways: Enter their name followed by "youtube channel" in the search bar at the top of the page. Click Enter and then select their channel from the list of results. Navigate to your video, locate the comment made by this individual, and then click on the person's YouTube user name. This is located below the individual's header and username. Find this to the left of Send Message. This user is no longer able to comment on your videos. This also prevents the user from sending you a message through YouTube.
Navigate to youtube.com. Sign in to your account. Navigate to the individual's YouTube channel. Click on the "About" tab. Click on the flag icon. Select "Block User" from the drop-down menu.