The External Hard Drive Shows Up as 'Read Only' on Mac, Help! Open Disk Utility > Select the external hard drive and click 'First Aid' > Click 'Run'.
Right-click external drive > 'Get Info' > 'Sharing & Permissions' > Check 'Ignore ownership on.'. Open 'Applications' > 'Utilities' > Launch 'Disk Utility' to 'Erase' external drive > Restore formatted data.