Follow the below steps to switch credit note voucher window from the payment window:-

Go to Accounts > Payment > When cursor stop on voucher number user have to press "F6" key > Credit note voucher entry window will be appear > Create voucher as per the requirement.

>>If cursor not stop no voucher number so then user have to follow below steps:-

Go to Master > MargSetup > Control Room > Search in all > Search -- "Voucher No" > Click on Accept > There is one option shown > "Voucher Number Y-Ask N-Automatic" ---Change that option as "Y" > Then press esc key and save. 

Alternative Solution:-

Press "CTRL+J" on payment voucher window > Switch Over window will appear > Select Data Entry > Marg Erp 9+ Accounting window will be appear > Select Double Entry System > Type window will be appear > Click on Credit note option > Credit note voucher window will be appear >Then generate credit note voucher .

NOTE :-CTRL+J Option can be use anywhere in the software.