The Linxdot has an instant sync feature that pulls a fully-synced snapshot every time the hotspot falls behind the blockchain by 50 blocks. This is an automated process and it requires no attention.
In case Explorer (explorer.helium.com) or the iOS/Android app indicate that your Linxdot is still syncing, that would be due to the Explorer not updating this information in real time. Allow between 12-24 hours for the sync status to update. In many cases, your Linxdot will start getting witnesses and issuing challenges (only possible when synced) before the Explorer even reports the hotspot as synced.
The sync and power status of a hotspot update through a process called peer to peer gossiping. This happens by itself a few times a day only.