Step 1) Go to Master > Account Master > Account Master.
Step 2) Add a New Account.
Step 3) Select Account Category as GST.
Step 4) Click on the GST Option .
Step 5) Select Cess in GST Type.
Step 6) Then Select Tax should be Both.
Step 7) Select Cess Based on Amount , Qty. And Both.
Step 8) Then Cess allowed to YES in the Environment setting.
Step 9) Also Add cess in the HSN/SAC master.