ChromeProfilesWorker.ChromeBinaryFileName
https://github.com/ToCSharp/AsyncChromeDriver/blob/862d692960532895670074d8b915529474b4f37b/AsyncChromeDriver/ChromeProfilesWorker.cs#L21 . You may change it
asyncFirefoxDriver = new AsyncFirefoxDriver(new FirefoxDriverConfig().SetHeadless().SetWindowSize(1200, 900));
webDriver = new WebDriver(asyncFirefoxDriver);
await webDriver.GoToUrl("https://www.bing.com/");
var screenshot = await webDriver.GetScreenshot();
using (MemoryStream imageStream = new MemoryStream(screenshot.AsByteArray))
{
System.Drawing.Image screenshotImage = System.Drawing.Image.FromStream(imageStream);
screenshotImage.Save(@"C:\temp\screenshot.png", System.Drawing.Imaging.ImageFormat.Png);
}