NTFS (NT File System) is used in Windows Operating System, When you plug an external drive with NT File System on a Mac, you can read datas from the volume but macOS does not have write support for NTFS.
This is a simple method that can be used with macOS to gain read/write access to Windows NTFS on macOS.
Mounty is is a menu bar application.
Install Mounty and Open Mounty
Drag and Drop Mounty app into Applications folder and open it from LaunchPad.
Re-Mount Volumes from Menu Bar Icon
From Menu Bar Icon, Mount NTFS Volume as writeable.
Fact to Consider
NTFS does not play well with macOS. You have to Safe Eject Volume from Finder, Otherwise the volume may become un-mountable with macOS.
You might have to plugin on a Windows computer to Fix and Repair volume. You can not use Mounty to Erase a Volume as NTFS with Disk Utility.
You have to use alternative paid drivers like Paragon NTFS to gain additional Access.