How how assign serial nos to FG Qty ?

Dear Experts,

we have all FG materials with serial no profile,Material code creation team forgot add serial no profile to 1 FG,and production order [ 20 qty] and Goods receipt completed for order qty[5 qty].stock of FG get updated without serial nos,during the time serial no profile is added by Material code creation team then for next GR against production order stock of FG get updated with serial nos[ 15 qty].

we are trying cancel old GR [ Material document without serial nos ] but system is asking for serial nos,when serial nos added error for serial nos status is appearing.

Please advice how assign serial nos to FG Qty [ 5 qty without serials nos ]

Thanks,