Yes you can use Nair on your Vagina but just avoid getting any Nair inside your Vagina otherwise it can lead to infection.
Just spread the Nair onto the hairy parts of your Vagina that you want to remove hair from and then use it like normal.
If you have sensitive skin then test a small area with just a bit of Nair before using too much Nair on your Vagina.
I've used Nair on my Vagina before to remove hair from my Vagina and it has been no issue.
Just avoid getting any Nair inside your Vagina and you'll be fine.
You could also just shave the Vaginal hair but sometimes that becomes itchy and then Nair would work best at hair removal from your Vagina.