remove dot at end of text

You can remove any dots at the end of a string using the TrimEnd method:

str = str.TrimEnd('.');

You can use the Substring method to remove only the last character:

str = str.Substring(0, str.Length - 1);

If the last character should only be removed if it's a period, you can check for that first:

if (str[str.Length - 1] == '.') {
  str = str.Substring(0, str.Length - 1);
}