How to start in safe mode?

It won’t accept my known power-on password. Something in “Mail” locked and I had to do a power shutdown. Now, I can’t get it to come back on. The Shift key did get me to “Safe Boot.”

It opened with the blue screen, Safe Mode and data upper right, and the 2 fields for ID and password. But it didn’t solve the problem. It is not my Apple password I need but the “laptop “ password. So I can’t get it to open to get to my “users” password.

Had to spend an hour on the phone with Apple support (who were great) to solve this one.