Read the documentation of the library you are using. Call/email the support desk of the library you are using. Use a tool such as
JustDecompile[
^] to decompile and read the code of each Method. Try all overridable Methods until you get the right one (the Method you want may not even be overridable). Make a random guess. At least tell us which library you are using (if it is something we might know) so we might be able to tell you.
Pick one! ;)