There is no such thing as "facility GMP certification" for FDA Class II devices. Various rules exist; some of those are called the "GMPs". You are required to conform, and in the case of a 510(k)ed device to declare that conformance, but not otherwise required to prove that conformance, prior to initiating marketing.
Whoever prepared and filed your 510(k) must already have known this answer. Consult with that person, as there are many other things of which to be aware.