Hi,
You can transfer the material through movement type 301(Plant to Plant) by MB1B Tcode.
If you want to transfer through STO, then follow this .
1) STO in ME21N.
2) Outbound Delivery in VL10B.
3) PGI in VL02N
4) GR in Receiving Plant in MIGO
Please inform if any more help is needed.
Regards
Binoy