After you create a user function (Insert > Expressions, Functions and Variables > User Function), you see the function in the details view
with Option set to Interpolation
(Data Input).
To import data from a file, set Interpolation Data > Option as appropriate, then right-click in the Interpolation Data list and select Import Data... from the shortcut menu. This displays the Import Interpolation Data dialog box, where you specify a file name.
For 1D data, Column Selection fields appear. You can select which column of data in your import file is appropriate for the coordinates and values.
For 3D interpolations, columns are selected in the same way, with X, Y, and Z data all required.
Each line of the file must contain numbers, separated by a space or comma.
Once the data is read into CFX-Pre, the values will be written directly to the solver input file and the data file will not be read again. If its contents are changed, then you must return to CFX-Pre and explicitly import the data again to update the stored values.