Migrate from Standalone Instance to Failover Node Instance
This is not really advisable. Install and validate your WSFC then install and test the clustered SQL Server instance on each WSFC node. SQL Server can be really picky about installing to additional nodes of a WSFC cluster and you could easily find it failing leaving you with a one node cluster.
Also storage has a level of indirection for a cluster with ownership of a disk(s) that contains the datafiles for an instance being passed around as necessary.