How to make what if parameter 1 display Feb 2021 ?

Hi All

i have a what if parameter field.

Now it can display 0 till 12.

when i click on

1 which is current month -1 , i need it display = Feb 2021 

2 which is current month -2 , i need it display = Jan 2021 

3 which is current month -3 , i need it display = Dec 2020 

and so on

Below is my PBI file :-

https://www.dropbox.com/s/tc0egzf81m65hsi/PBT_V2021_392%20TI_SI_GL%20how%20to%20make%201%20display%20Feb%202021.pbix?dl=0

Paul