Either you scan network assets which are reachable from your Lansweeper server (this requires that
ports required for scanning are open) or you use LsPush. This is a small executable which scans a Windows computer and sends the result back to your Lansweeper server using direct server connection (port 9524/TCP by default), file share or mail. You can find details
here. It is possible to configure a scheduled task for running LsPush and deploy it via group policy.
Alternatively you could consider installing a local scanning server at the remote site and connect it to your central database server. This only requires a database connection (port 1433 TCP and UDP by default). You could stop Lansweeper service on the remote scanning servers during times where you have no connection at all. For multiple scanning servers you need a Lansweeper Ultimate, Corporate or MSP license.