As you might know, there is not yet specified way for a software update over the Bluetooth Mesh. This is high demand feature and for sure it will come. However, if this feature is needed just right now and your product uses Apache Mynewt, there is a way to mitigate the issue.
Apache Mynewt supports Bluetooth 5 features and in particular the one called Advertising Extensions. It gives a way to support multi advertising and this gives an idea to have advertising instance dedicated to Mesh operations and in the same time an instance which will allow to connect for the software update purpose.
This tutorial will guide you through configuration and simple update of firmware over BLE on Mynewt of Mesh node supporting Generic On/Off model.