sign out from secondary authentication account

 a ) Open system preferences > click on iCloud and click on sign out , you can see a window stating do you want to keep a copy of your iCloud data on this Mac before signing out ? The boxes iCloud Drive , contacts , calendars , reminders are checked by default - so click on keep a copy . A pop up window will appear are you sure you want to stop updating and continue with sign out ( any documents not updated to iCloud Drive , will be moved to a folder named “ iCloud Drive archive in your home folder on this Mac ) so don’t click on “ cancel “ but " click on continue with sign out ."

 A pop up window will appear . Do you want to keep a copy of safari passwords on this Mac ? 

    ( 1 ) Delete from Mac ( 2 ) cancel ( 3 ) keep on Mac .So its optional you can select keep on Mac or click on delete from Mac ( as some users write down the safari passwords in a safe place and they can autofill it again . ) 

( b ) It will prompt enter the Apple ID password for mail address to turn off find my Mac , so enter your Apple ID password and click on continue , a small circle will rotate , be patient .

In the upcoming screen shot delete the Apple ID completely from the box .

Then type the Apple ID address used with 2FA in the field 

( a ) A pop up window appears a verification code is required .

  ( 1 ) text …..your trusted mobile number is written .

   ( 2 ) can not use any of these numbers , if you check the box of can not use any of these numbers and click on continue , a pop up appears Apple ID account recovery if you do not have access to these phone numbers it may take up to a week to regain access to your account ( 1 ) cancel ( 2 ) start recovery , so click on cancel .

You have to click on text number , enter your verification code sent to trusted number …..the circle rotates and you will see a small circle is also rotating in the field of Apple ID .

( b ) enter your admin password and click on ok wait for a while again a small circle rotates , a pop up window appears in which the box for use iCloud for your documents and data , use find my Mac are checked , so click on next .

( c ) A window appears allow find my Mac to use this location of this Mac ? Click on allow you can see in system preferences - 2FA id is shown , check the box of Siri and after few minutes click on options button in front of iCloud Drive and check the box of desktop and documents folder and click on done .

( d ) Again click on account details , check the section security , click on plus sign to add more trusted number and click on done , the number will be verified , now you can see 2FA is having green dot in front of it and you can use the two factor authentication .

Secondary authentication account for an Apple ID is in which three security questions and answers are created ,

In my system preferences > iCloud I have signed in with mail address say example1@gmail.com - this is my Apple ID created with security questions and answers .

See this article https://support.apple.com/en-in/HT201363

Apple uses security questions to provide you with a secondary method to identify yourself online.

I had also created an Apple ID using 2FA previously , say example2@icloud.com

Now I just want to sign out from my first Apple ID account and sign in with 2FA in my Mac the location will be same as system preferences > iCloud and in my Mac I will be using id created with 2FA .The reason for it I love exploring new methods sign out from first Apple ID account and then establish new account using 2FA , then in few days revert to the same / different account .

The users must always write down each web mail address and their respective passwords in their diaries .

In the upcoming steps , if they had clicked on delete from Mac they will be deleted , but that will be filled when keychain is set up , and say a web site is opened , you have to click on save the passwords or a web mail account is configured .

It's the choice of a Mac user which option to select , passwords written in diaries is always recommended .