There are a large number of ways to promote, from the basics of understanding the work of Youtube algorithms to contacting channel development agencies, but this is a paid story and not always working.
I recommend looking for information on this forum. If you think logically, everything is simple. You need subscribers to develop a channel, right? It is necessary to understand where to get subscribers (traffic). We are looking for a resource suitable for the topic of the channel, or we go a more complicated way and create such a resource. There are really many options.