Mental health is a great subject to base your videos on. It's a very important subject which some people treat as taboo.
The best you can do when starting out is to make informational videos and videos with some light advice or options for people which could point them in the right direction. Ask people at the end of videos to share your videos with someone who might find the videos helpful.
Another method is to optimise your channel's tags and metadata, get people to share things. There are international days for different states of mental health which is useful for promoting your videos to help people and also good for spreading information to people.
Thanks for sharing and all the best.