Hi @mohiniu12161390,
When you configure the SFTP for daily load, it automatically picks the files that are modified/added after the previous run date. So any specific reason why you want it to be defined externally? Also, I believe if you have selected the folder in your configuration it will monitor the entire folder for the file changes - just ensure that the file format is the same for all the files in the folder.
Triggering the journey can be done via the segments. I don't think you can start the journey based on the file load.
Alternatively from AJO, you can fire APIs so see if you can fire API and get the alert status and take action within the journey.