Click on Setup Tax Types (Sale).

A new window will appear on your screen. Two fields for GST: Use for GST and GST Type Added. If you are creating tax type GST, select CGST/IGST in the GST Type field. Similarly, IGST field for tax type IGST. Use for GST field will be same in both cases CGST/ SGST and IGST See the window below:

                                                                  Fig 1. Setup Tax Type (Sale)  

Click on the 'Save' button.