I configured an external hard drive on a laptop that I no longer own. That user appears to be the only one having read and write permissions because of the settings I made. As a result, my Mac believes that I am a user with read-only access. Is it possible for me to modify the permissions on my Mac so that I may write files to the external hard drive and have proper access to it? I really want to be able to utilize it correctly.
Did you use the drive on a Windows PC? You may format the drive as NTFS on Windows, and NTFS is a read-only file system on macOS. Thus, you can check the file system of that external hard drive in Disk Utility.
If it is an NTFS drive, you can either use an NTFS driver for Mac or reformat the disk with a macOS-compatible file system such as APFS and Mac OS Extended, to use the drive on both macOS and Windows platforms, choose exFAT or FAT32.
NTFS drivers for Mac such as iBoysoft NTFS for Mac can automatically mount the NTFS drive in read-write mode, this is best for users who don’t want to erase the drive to lose data.