doing 2023 taxes it will let me enter 2023 dates for self employment

Start date 01/01/2023 Fiscal year must start in 2023 or 2024 Fiscal year must start in 2023 or 2024 dd/mm/yyyy End date 31/08/2023 Fiscal year must end in 2024 or 2025

Self-employed

If you don't have a specific reason to change your fiscal period, then you should just use 01/01/2023 to 31/12/2023. Don't enter the slashes, just put in the numbers.