I have a string that I converted to a TextInfo.ToTitleCase and removed the underscores and joined the string together. Now I need to change the first and only the first charact
You just need to lower the first char in the array. See this answer
Char.ToLowerInvariant(name[0]) + name.Substring(1)
As a side note, seeing as you are removing spaces you can replace the underscore with an empty string.
.Replace("_", string.Empty)