Turnover doubt in 2017-18

a party has shown 2.93cr turnover during 2017-18 but have not filed VAT return. GST turnover shown GSTR 3B only 89 lakh. GSTR 1 also in same. GSTR-9/ 9C not filed in said FY. Please give me suggestion for derived the actual turnover of that unit for GST period? because it's quite impractical that all turnover
2.4cr pertaining to VAT period only.