First you need to make sure you have selected the Form Data Model Prefill service for your form as shown below

Then you need to change the binding fo your FDM from literal to Request Attribute. The string in the binding value can be any name. For example I have put accountnumber here. This accountnumber will be used in the code in the jsp page

Next, you need to create a NEW AF Template and Page Component as shown in this video https://helpx.adobe.com/experience-manager/kt/forms/using/saving_and_retrieving_adaptive_form_data.html#CreatenewAdaptiveFormTemplateandPageComponent
Saving And Retrieving Adaptive Form Data . It is recommended that you use the same page component that is provided in the article
Create your AF based on this new template. Associate your Form Data Model with this form
this is the best practice for your use case since we are going to populate the form based on url parameter
Then in the worker.jsp replace the code with the following code
Map<String,Integer>map = new java.util.HashMap<String,Integer>();
if(request.getParameter("accountnumber")!=null)
{
System.out.println("There is a accountnumber parameter in the request"+request.getParameter("accountnumber"));
map.put("accountnumber",Integer.parseInt(request.getParameter("accountnumber")));
slingRequest.setAttribute("paramMap",map);
}
When your AF is being loaded this code will get executed. This will check for accountnumber parameter(This needs to be the same as you have specified in the above screenshot) parameter in the URL. We then create a map with the appropriate values and pass the map in the slingRequest. This will populate your for with the results from the FDM get method
for example when you load an AF with the following URLhttp://localhost:4502/content/dam/formsanddocuments/forumsdemoform/jcr:content?wcmmode=disabled&accountnumber=37
http://localhost:4502/content/dam/formsanddocuments/forumsdemoform/jcr:content?wcmmode=disabled&accountnumber=37
The form will fetch data associated with accountnumber 37 and populate the form
Let us know through this forum if this works or you have any more questions