Create a new user account in users and groups by clicking on plus sign , name an account and enter its password .
Take cursor on apple logo and log out from your old user account and then enter the credentials name and password on the screen of your new user account .
( a )The window is showing data and privacy , click on continue and sign in with your Apple ID ( fill up the credentials ) and click on continue .
( b ) Again enter your Apple ID and password and click on continue .
( c ) A prompt will appear on the screen use two factor authentication ( its optional you can uncheck the box and click on continue ) .
( d ) A pop up window will appear do not upgrade Apple ID security and upgrade iCloud security , so click on do not upgrade .
( e ) A small circle will be rotating , setting up account will be shown , wait for a while and options will be shown would you like to set up iCloud Keychain ( 1 ) set up iCloud Keychain ( 2 ) set up later , you can click on set up later and click on continue .
( f ) A window will appear showing enable ask Siri , keep the box checked and click on continue .
( g ) Another window will appear all your files in iCloud stores files from documents and desktop in iCloud Drive , so check the box of it and click on continue .It will show setting up your Mac , three right check marks will be shown .
( h ) Open system preferences and click on accessibility > trackpad options , check the boxes of scrolling with inertia and enable dragging with three finger drag and click on ok ( as drag and drop feature always help a user in every way ) .
( I ) Again in the system preferences > click on I cloud you will see the box of keychain is unchecked , so check the box of it after a while a prompt will appear enter you Apple ID password to set up iCloud Keychain so fill up the password and click on ok .
( j ) Again a pop up window will appear to set up iCloud keychain on this Mac , request approval from one of your other devices using iCloud Keychain .( 1 ) use code ( 2 ) cancel ( 3 ) request approval , so click on use code .
Now , I don't remember the code how to proceed .