You need to
- take a backup of your current database, as explained in this KB article
- perform a new installation of Lansweeper in advanced install mode, choose SQL Server as database and connect to your SQL Server cluster. Either run the installer under an account which has sysadmin permissions on your SQL Server or choose SQL Server authentication
- restore your database backup onto the new database
This KB article provides aggregated instructions on how to move your database to a different server.
Note: You don't need to run the installer directly on the database server. It is enough to provide the SQL Server hostname\instance name during the installation process.