I know which electrode is the reference electrode, and I also know the time point (s) and sampling rate corresponding to events
In the file formats listed in the import dialog window, select "EEG: Matlab matrix".
To learn how to use Brainstorm for processing EEG, start by following the introduction tutorials at least until #19 using the example dataset provided, then follow the advanced tutorial EEG&Epilepsy.
https://neuroimage.usc.edu/brainstorm/Tutorials
Thank you very much!