You need to go to the SouthWest Florida water management district web site: https://www.swfwmd.state.fl.us/recreation/how-make-reservation
Click on the Alston Tract link: https://www.swfwmd.state.fl.us/recreation/alston-tract
You will need to setup an account with the WMD (free) and pick your dates, etc. They will respond with an e-mail and also confirmation on screen if your reservation is confirmed. By the way, as of December 2020, you can only make reservations 30 days in advance.