Hi Tiago,
As I understand you are trying to load data in .txt file into Simulink model. The function textscan should be able to do this for you, it reads data from an open text file into a cell array. You can try put this function call into the model callbacks, for example 'PreLoadFcn' or 'InitFcn'. Check the documentation of model callbacks for how to use it.
To learn more about import txt file into MATLAB, check the domumentation of Ways to Import Text Files
