How do I add/edit 'digit' property into PGAdmin4 ?

Hi all,

I need help to change an existing column in my table from text to 'digit' type.

However, I can't find any numeric or integer property type.

The digit type should contains numbers only but it is not for calculation.  It is a zipcode that has 6 digit numbers.

Please let me know how do I alter the text type to digit type.  If alteration is not possible, how do I add in the
propertyinto PGAdmin4 which is running on windows 10.
 

Thank you.