Well, to become a GIS officer after your graduation in Geography there are basically 4 steps:- 

1) Obtain Postsecondary or Diploma training in GIS Technology - This means you have to get a graduation or a diploma course in GIS Technology, a lot of colleges have these courses. 

2) Seek Employment - As a GIS specialis, you will have to do mapping and other such thing, so, they always look for people with a graduation in principles of geograph, etc. and also a few years of experience. 

3) Obtain professional credentials - Get certified in the various fields available under GIS under esteemed institutions.

4) Pursue further education or look for better jobs.