From asensei app version 1.11 onwards, during a workout, asensei will automatically attempt to reconnect to your PM5 should the connection be lost for any reason (such as walking out of range temporarily).
However please note that on some PM5s with Hardware Version 600 or higher you will need to update to firmware version 169 or higher. In general we would always recommend running your PM5 on the most recent production version of the firmware.
To update the PM5 firmware you can use the Concept 2 Utility app on your PC or Mac - see here for more details.
In addition we would alway suggest you check you are on the latest version of the asensei app by checking in the Apple appstore and upgrading if required.