Mold discovered on Mattress botttom once opened from box and plastic bag covering it.

We upgraded from a Full sized Bob-o-Pedic memory foam mattress to a queen in March of this year- 2020.  As we were quarantined due to COVID-19- we did not open the box or the Plastic covering the mattress until May 15th. As we were starting to cover the Mattress with the Goof Proof covering we noticed Darkish spots under the Mattress zippered covering.  After unzipping the cover and investigating further- we discovered there is indeed black moldy splotches all over the bottom of the mattress.  Please advise as what is our next step to correct this issue please.  Thank you!

SIncerely,
Lydia M. Lucas