MeldaProduction offers a free version of their MPitch plugin, which is a simple pitch correction and manipulation tool. You can download it from their website:
Assuming you have downloaded FL Studio via the official free trial link, here is how to get Pitcher running on a vocal track. pitcher vst plugin free download link
Based on the text provided, you are likely looking for by Auburn Sounds, which is the industry standard for a "pitcher" or pitch-correction plugin. Another common option is the classic GSnap . MeldaProduction offers a free version of their MPitch