Excel data arrangement

I need the daily closing price for 50 Indian companies 120 days before their merger announcement and 20 days after their merger announcement, found and arranged. I have all the Excel data files containing the daily closing price for all BSE companies, the file containing the list of Mergers and their announcement date, and the input excel data sheet where the closing prices should be pasted in. The Excel file containing the closing price is large (1.1 Gb & 300 Mb), therefore please make sure that your laptop/computer will be able to process the files comfortably.
I will provide a video to explain how to extract these details afterwards for reference. I NEED IT BEFORE THE 18th OF FEBRUARY.