I forgot my Macintosh HD password I need to reinstall my iOS

Hello Jomh1212,

It sounds like you may be referring to the password you're prompted to enter if you've encrypted your startup disk. If so, Use FileVault to encrypt your Mac startup disk has some options that may help.

"If you lose both your account password and your FileVault recovery key, you won't be able to log in to your Mac or access the data on your startup disk.

Change your recovery key or reset your password

To change the recovery key used to encrypt your startup disk, first turn off FileVault, which requires your account password. You can then turn it on again to generate a new key and disable all older keys.

If you forget your account password or it doesn't work, you might be able to reset your password."

If this isn't the issue you're having, please provide more details about the password you're being prompted for.

Regards.