Install your D16 plugin directly from the Splice desktop client.
Once installed navigate to FL Studio go to:
On the left, you can add plugin search paths, add the location you installed your D16 plugin to and hit Start scan. The default installation path is:
C:\Program Files\VSTPlugins\D16 Group\
Please note the D16 Rent to Own plugins only support 64 bit DAWs, there is no 32 bit version.