How can I reset Mac recovery key from my iPhone?

The instructions for Account Recovery under Two-Factor Authentication should have been sent to you. See below.

“If you can’t sign in, reset your password, or receive verification codes, you can request account recovery to regain access to your account. Account recovery might take a few days or longer, depending on the specific account information you can provide to verify your identity. “After you request account recovery, you'll get an email with a confirmation of your request and the date and time of when you can expect to regain access.” … When the wait period is over, Apple sends you a text or automated phone call with instructions to regain access to your account. Follow the instructions to immediately regain access to your Apple ID.”