GST RETURN NILL FILE BUT MORE THAN DEPOSIT IN BANK 1 CR

A dealer came to me, he having wholesale business of fruits (banana) also registered with GST, his accountant file NIL GST return through out last financial year 2022-23, but in Bank Current Account total cash deposit during the last financial year is  more than 1.72 Crore. Income tax return till not file – please advise what to do now ?