How Much GST can return deducted by Bank on DSA Commission

My friend runs a DSA business for various banks and earns a good commission. However, he has office expenses to manage. The banks pay his commission after deducting 18% GST and 5% TDS. Can he get a refund of the deducted GST, and what is the process for this? The significant deductions are causing a shortage of funds for his other office expenses.