Could you please clarify what would you like to do? Generally, fixed-price contracts can consist of multiple milestones that are added, funded and then released to the freelancer once they complete the work. You can find a lot of information and a video about how it works here.
I checked and see that you already have a fixed-price contract that you can access here and see milestones that have been released as well as upcoming milestones that are pending funding.
Please, let us know if you need further assistance with this.