You have two choices, i.e. 1) For most steels, if you have an analytical solution, you can input n and t value (no other variables); 2) you can also input the digitized data, which is contained in one file.
If you want to input the FLD as a file, it format is:
a) First line: The title of the file, any name is good.
b) Second line: n x 2 (n is the line of the strain data as in the following)
c) The following lines (n lines) are the strain data: minor strain, major strain. It is possible for you to input as many lines as possible, as long as the value of n is specified correspondingly.