There was a power outage while writing into the Mac external hard drive

While writing into the external hard drive, there was a power outage. Now, i do not want to start all over again instead point it to the same folder in the external hard drive to continue where it stopped.

The corresponding code using Microsoft was as follows and it resumed from where it stopped. How can I do it in Mac.

C: \Users \mr>"C: \Program Files \application.exe" -datadir=R: \folder_index

where R is an external drive. any help would be greatly appreciated. We can quickly connect thru a call / screenshare to complete it.

[Re-Titled by Moderator]