The host application probably still exist on your iSeries. Have you verified using DSPFCNUSG?
If it’s still there, there is nothing to recover, just a problem accessing with the iNav gui. Try installing the latest iSeries Access for Widows cume SI35287 and check all your authorized options when you install.
I did verify the Function Usage in my system, and the funcion QIBM_EJB_SERVER_FUNC is missing. Do you knkow how can I recover it?