If you want to resume a partially downloaded torrent file, you can use the Force Recheck option. This option will scan the file and check how much of it has been downloaded. Then, it will continue the download from where it left off. To use the Force Recheck option, follow these steps:
Long press on the torrent file that you want to resume.
From the context menu that appears, tap on Force Recheck.
Wait for the scan to complete and then start the download again.
You can see an example of how to use the Force Recheck option in the image below from 
Torrent Pro.
