If you are connected to another device (from the Settings > Connect device menu option), you can browse the content on other devices (assuming they haven't disabled that setting in the Connect devices settings page)
When synchronising your devices in this manner, it is crucial that your songs are correctly indexed and do not have missing UUID (unique identifier ) and last modified date information. You will be warned if this is an issue before proceeding. This is to keep a record of matching songs and the dates they were last modified.
Once you choose the device, it will prepare a list of available items for you (songs, sets and profiles). You can then choose which items to download and they will be added to your device.
Note that only songs will show items as needing updated since sets are not indexed in the app.