Refer to these instructions:
Use Disk Utility to erase an Intel-based Mac - Apple Support
The solution is to erase the internal storage device.
What does that mean? In the OS X Utilities screen (or macOS Utilities whichever one appears), choose Disk Utility. Then, be sure to select the View menu > Show All Devices.
- The "device" in this context means the upper left-most device in the list — the one with an immutable name such as Apple SSD Media or some such. Erase that.
Then, quit Disk Utility, return to the Reinstall Mac OS X (or macOS) menu option, and determine if an eligible device appears.