How exactly did you export and what is the exact format of the files? Exporting hand histories from PokerTracker 4 does not generate an excel file (csv). In PokerTracker 4 you can export hand histories via the right-click menu in a hand report (Export Original Hand Histories) or
via 'Database -> Export Hands' and these will be .txt files. Exported hand histories can be reimported into PokerTracker 4 via 'Play Poker -> Get Hands From Disk'. You can can export reports via the right-click menu (Export Report) which will be .csv files for use in programs like Excel however if you exported a PokerTracker 4 report you cannot reimport hand histories from that file.