One of the many ways to do that, is to use Social Media - Facebook, Twitter, Instagram, etc.
On Facebook, try joining groups relating to your content. For example, I post Unity Game Development tutorials primarily. I've joined many Game Development related groups on Facebook. Whenever I publish a video, I post in all of these groups.
On Twitter, whenever I tweet any of my videos, I always use relevant hashtags, so that people find my tweets more easily. There are also Twitterbots that automatically retweet tweets that contain a certain hashtag, so that really helps get your tweet to a larger audience.
On Instagram, post your channel link in the bio of your Instagram profile. Then you can post a screenshot of your video, saying "so and so video is up, channel link in bio". Don't forget to use relevant hashtags there as well. Those hashtags are what will help get your content to more people.
Hope this helps.