value attribute on the lightning:inputField tag can be used to set field values on lightning:recordEditForm. Check the following sample code for reference.

Sample Code:

Sample.cmp:

<aura:component implements="force:appHostable" >       
    <aura:attribute name="AccountId" type="String"/>       
    <div class="slds-box slds-theme_default">           
        <lightning:input type = "text" value = "{! v.AccountId }" label = "Account Id"/><br/>  
        <lightning:button label = "Create Opportunity" variant = "brand" onclick = "{! c.navigateToNewRecForm }"/>       
    </div>       
</aura:component>

SampleController.js:

({  
  
    navigateToNewRecForm : function(component, event, helper) {  
          
        var evt = $A.get("e.force:navigateToComponent");  
        evt.setParams({  
            componentDef : "c:NewRecordForm",  
            componentAttributes: {      
                  
                AccountId : component.get("v.AccountId")  
                  
            }  
        });  
        evt.fire();  
          
    }  
      
}) 

NewRecordForm.cmp:

<aura:component controller="NewRecordFormController">        
    <aura:attribute name="AccountId" type="String"/>  
    <aura:attribute name="AccountRec" type="Account"/>       
    <aura:handler name="init" value="{!this}" action="{!c.doInit}"/>       
    <div class="slds-box slds-theme_default">          
        <lightning:recordEditForm  objectApiName = "Opportunity"  
                                   onsuccess = "{! c.handleSuccess }"> 
            <lightning:inputField fieldName="Name" value="{! v.AccountRec.Name }"/>  
            <lightning:inputField fieldName="StageName"/>  
            <lightning:inputField fieldName="CloseDate"/>  
            <lightning:inputField fieldName="AccountId" value="{! v.AccountRec.Id }"/>          
            <lightning:button class="slds-m-top_small"   
                              variant="brand"   
                              type="submit"   
                              name="Create" label="Update" />  
        </lightning:recordEditForm>  
    </div>  
</aura:component>

NewRecordFormController.js:

({  
  
    doInit: function (component, event, helper) {  
          
        var action = component.get('c.getAccount');  
        action.setParams({  
              
            acctId : component.get("v.AccountId")  
              
        });  
        action.setCallback(this, function(response) {  
              
            var state = response.getState();  
            if ( state === 'SUCCESS' && component.isValid() ) {  
                  
                component.set('v.AccountRec', response.getReturnValue());  
                  
            }   
              
        });  
        $A.enqueueAction(action);  
          
    },  
      
    handleSuccess : function(component, event, helper) {  
          
        var params = event.getParams();  
        alert(params.response.id);  
          
    }  
      
})

NewRecordFormController.apxc:

public class NewRecordFormController {  
	  
	@auraEnabled  
	public static Account getAccount(String acctId) {  
		  
		return [ SELECT Id, Name FROM Account WHERE Id =: acctId ];   
		  
	}  
  
}  

Output: