If it's running on the same machine as the v7 client, it's easy. Just go to Clients -> Add v7 Client. Give it any name it will take, address can just be localhost, or 127.0.0.1, then hit test connection, it should validate, and click OK to save.
Once you have it added, you'll want to save your Configuration so you don't have to add it back every time you open HFM.
Once you save the Configuration, you can set it to auto-load on HFM launch in the Preferences. Edit -> Preferences. Then 'Startup & External' tab, check Load Configuration File, then just browse to where you saved your configuration file.