IFS Assyst : Hide Digits in event Forms

Hi All, 

How to mask first 6 digits of a 10 digits number added in a field of event raised by a customer. 

Digits should be hidden from the service desk ticket in assystWEB.

i.e. 

Number to be hidden:

SSN : 1234567890

After hidden:

SSN : XXXXXX7890

Kindly advise.

Regards,

Nuwanthika