Help to Recover IMEI of Z831

Hello, have here a Z831, the customer go with the phone to some workshop and try to unlock with Sigma, Sigma say Ok but IMEI go corrupted ... 0003000.... I try to repair with Sigma, i try to repair in EDL, FTM, etc with other Boxes... but persist in same imei.

I have the skb file obtained from the workshop... How i can recover the imei of this phone?

Thanks,