There are many functions for reading digitized sensor locations, e.g., mne.channels.read_dig_polhemus_isotrak — MNE 0.23.0 documentation. There is an extensive tutorial on coordinate frame alignment: Source alignment and coordinate frames — MNE 0.23.0 documentation. There is an example showing alignment of EEG locations with the template fsaverage brain: EEG forward operator with a template MRI — MNE 0.23.0 documentation. Please study those, try it with your own data, and let us know exactly where you are getting stuck.