While you don't necessarily require an ITR to purchase term insurance, your insurance provider may ask for your previous year's ITR details so it is wise to keep your ITR details handy.
Tax benefits are deductions and not reimbursements and you can only avail tax benefits on term insurance when you file your Income Tax Returns or ITR. Your ITR takes into account all the premiums and other investments you make and accordingly determines the income tax slab applicable to you. While a Financial Year lasts from 1st April to 31st March, they can be filed till 31st July of the subsequent year.
For the year 2020, the date for filing ITR has been extended till 30th November 2020 because of the COVID-19 pandemic.