There are many ways. You can use power query, tables, vstack(), LAMBDA tools etc. Are your .csv file consistently formatted (same number of columns, and the column headers in the same order)? What about your ledger time point balances and outstanding transactions at that time - How do you have those set up?
Is it the same account (20 months) or 20 accounts for 1 month?
Mr. Excel has a forum for power query, called Power Tools. You can also go there to find solutions if you choose that route.