Dell R620 - alternative memory configuration

i have installed 12x 16gb Ram on a dell R620
Of all the sticks installed 2 dont show up being the ones in , b3 and b4.
Performed all the fault finding to make sure it is the slot and not the ram stick. ( replacing ram between fuctioning slot and non functioning slot as explained in dell support)

Now that im certain that those slot for some reason dont work , the suggested configuration goes out the window.

To mantain the system balanced do i need to remove the ram from slot a3 and a4 ?
If i need to do so , can install those 4 stick of 16gb ram previously in a3 a4 & b3 b4 to to a7 a8 & b7 b8 ?? would it be still balance ?
Or alternatively , is there a way to revive the dimm slot , some trade trick in the sleeve ot field tech, ?

can someone explain how to make informed decision based on this server architecture please thanks:

Sources
dell support answer 2018 by Dell-Daniel My
dell power edge memory
sample memory config
r620 owner manual


QUESTION NUMBER 2

i have removed and get rid of a MD1200
i still have installed in the r620 the perc810 but is not longer in use or necessary.
At every boot i get the message that perc 810 lost his raid configuration , 
in bios im unable to change config cause of course the md 1200 is disconnected and i can not apply setting to it
in hardware config in bios - perc 810 cant see any option of help
pressing C i get in another perc config (showing 710 and 810  that doesnt seem to do anythin as well ( probably my ignorance make me say this) . 
How can i get rid of those message at boot regarding loosing perc config ???

thanks youuu