Hello. I'm trying to lose pre baby weight. Is it true that Apple cider vinegar is good for weight loss?

Not really. Unfortunately I think this is somewhat of a fad diet. I am not aware of any evidence that apple cider vinegar does anything to increase metabolism or aid weight loss. Sorry.
No easy solution. There are some people who tout apple cider vinegar as the greatest thing, however I've yet to see any significant results. There is something to be said for the 'power of belief' so that is likely part of it. The best way to lose weight though is the hardway -through control of diet (avoiding excess fats/sugars, esp sugary drinks) and exercising well. If you build muscle, it helps with weight loss.