How to Choose between old and new tax regime for Tax Relief u/s 89

I have opted for the old tax regime from F.Y.2015-16 to the last F.Y. 2022-23 now I received some arrears of that financial year.And in this F.Y.2023-24 I want to opt for a new tax regime.My question is 1) while calculating the tax relief
u/s 89, software ask to choose between old and new regime. On choosing the old tax regime I got more tax relief than the new regime. but I am opting for a new tax regime in this financial year, what to do please guide.