72t Substantially Equal Periodic Payments early IRA distributions

On 7/1/23 began a 72t SEPP plan from my IRA. (I'm 58 1/2), but the advisors at the financial institution where the IRA is held tell me they can't answer any questions about the plan and I should ask a tax advisor. 🙂 So here's my question: I'm using the RMD Universal Life table. I understand that with the RMD method, the distribution amount will change each year according to the account balance on 12/31 of the previous year, but how does that change occur? Is it automatic somehow or do I need to fill out a new distribution form with the new calculation each year? Assuming it's on me, can I file the form at any time before July 1 each year?