If you try to encourage them to be satisfied with the gender they were assigned at birth, they are not going to feel any better. That is going to feel invalidating. They aren't being groomed into becoming transgender, and knowing what transgenderism is does not automatically turn someone into a transgender individual. Your sexuality and identity don't just change like that.
I'm also not sure why you suggest transitioning is unhealthy, when being respected for their transgender identity improves mental health and reduces suicide risk drastically, and gender reassignment surgery is also associated with greater mental health benefits.
Again, the sucky situation for them is they are not being treated respectfully or equally. There are hundreds of pieces of legislation around the country threatening their way of life, from denying them healthcare as a minor, prohibiting participation in sports, prohibiting using the bathroom that matches their identity, banning discussion of their identity in schools and even attempts to investigate their parents for child abuse in Texas. This doesn't include the violence and harassment transgender people face, the income disparity and their overrepresentation in arrests.
The way to love your transgender loved one is to respect their identity, call them by their preferred name and use their preferred pronouns. They probably won't associate with you if you insist that they were groomed or are unnatural and need to change who they are.