mac

Hold down the power button until the Mac shuts down. Then hold down the Command and R keys and push down the power button and don't release the Command R keys until the Mac boots into Recovery. Then choose Disk Utility and run First Aid per the instructions in the first link I gave you.

Hi,

See the following for detailed instructions; note the order to repair volumes, container, then disk: How to repair a Mac disk with Disk Utility - Apple Support