Hi @Sabbir_Anwar ,I hope you are doing well.
See your question can be approached in 2 ways.
1)Firstly, if you are not sure which row your data should always start writing in its next run you can always pass the RowIndex as an asset value and provide it your write range activity. So whatever RowIndex is dynamically passed through assets it will right in that row itself nothing changes in code you have to do and you will have the control on which row it should write in.
2)Secondly, using append range activity instead of write range activity which will write your data automatically in the next empty row it finds.
Hope this was useful to you. Have a good day!
Thanks & Regards,
Shubham Dutta