Coverity issues for Filesystem path, filename, or URI manipulation in C#, .NET Core

Question

We had a Coverity scan performed in our code and found the issue related to "Filesystem path, filename, or URI manipulation" which is a high impact security issue.

This is the code we had at first:

var xxxFilesPath = configuration["FileSection:Path"]; 
qualifiedFileName = xxxFilesPath + input.FileName;

As per our research and understanding we have changed the code as below to resolve the issue:

DirectoryInfo xxxFilesPath = new DirectoryInfo(configuration["FileSection:Path"]);
FileInfo[] files = xxxFilesPath.GetFiles(input.FileName); 
input.FileName = files.FirstOrDefault().FullName;

But after running the scan, it is still showing the same errors (not resolved).

Technology details:

1. .NET Core 3.1
2. C#

I'm not sure if I'm working on correct area, in that case reason of the issue will be very helpful.

Could anyone let me know, what should be the correct step and why so.

Thanks in advance...