Just follow the steps below:
STEP 1:-
First go to WhatsApp settings > chat settings & make full backup of your chat.
STEP 2:-
After that go to phone settings >Apps >Whatsapp >Clear the data of whatsapp.
STEP 3:-
Now go to file manager and search for Whatsapp folder.
STEP 4:-
Now 'Rename' the Whatsapp folder to "OGWhatsapp".
STEP 5:-
Now Uninstall WhatsApp from your mobile.
STEP 6 :-
STEP 7 :-
Open ' OGWhatsApp'. Before verifying your number ,scroll down and click on Restore all data.
STEP 8:-
After that enter your old number ( which you use on whatsapp )
STEP 9:-
Next verify your number and Now you can access your old number WhatsApp account on your 'OGWhatsapp'.
STEP 10 :-
Now you simply go to Play store and download whatsapp ( download here )
STEP 11:-
open Whatsapp and create an account with new number.
All done . Now you can access two Whatsapp accounts in one device.
Enjoy!