omission of branch turnover

one of client has two branches in single state.As per gst both the branches turnover should be included in returns.but he forget to include and no turnover has been shown for one branch for the entire financial year..now the other branch filed all the returns.....there is no chance of including in 2018-19....now he want to update the 2018- 19 details in 19-20...here my question is whether these will be include in turnover of 2018-19 or 2019-20...