The conversion date is simply the date you start using Flare and discontinue using your previous accounting system. You don't have to enter the conversion date into Flare, but make a note of it.
Example: your fiscal year is January 1st to December 31st. You want to begin using Flare on June 1st. This is your conversion date. In your previous system, you would reconcile your bank statement and run a trial balance for the period January 1st up to and including May 31st. On June 1st, you'd enter account balances from the trial balance into Flare's opening balance form.
Although you can choose any date as a conversion date, we recommend that you reconcile your bank statement for a given month and choose the first day of the following month as the conversion date.