ios – Swift: Concern with passing knowledge from perform to a variable

I’m making an attempt to move knowledge from a perform to a declared variable,

   func request(platform:String, rankData:[String : [CustomModel]]) {
 
        
        APIService.shared.get(api: "someURL", parameters:[:], completion: { (outcome: End result<ModelResult,AFError>) in
            self.hideHUD()
            swap outcome {
            case .success(let success):
                
                rankData = success.outcome
                self.collectionView.reloadData()
                
            case .failure(let failure):
                print(failure.errorDescription!)
            }
        })
        
  
    }

however I get this error

Can not assign to worth: 'rankData' is a 'let' fixed

I added inout however nonetheless not working, additionally tried so as to add

 var aData = rankData 

however nonetheless, I can’t move knowledge to my variables and xcode give this warrning:

Variable 'aData' was written to, however by no means learn

any assist?