Which of User Exit or BADi could be used to populate equipment number in operation equipment field

Hi Experts,

I want to populate equipment number in the operation equipment field as snapshot shows. I have custom logics to populate sub equipment number, but I need to find a user exit or BADi to realize it.

I  found 2 BADi (ALM_ME_001_ORDER Order/Operation Data,  WORKORDER_UPDATE Business Add-In PM/PP/PS/PI Orders Operation: UPDATE ) from internet, however I am not sure whether these BADi are applicable for this requirement as I have less experience in ABAP development. 

Could you kindly help me have a look at  these BADi. If they are not applicable, is there other user exit or BADi which fulfill customer’s requirement?

BTW, if I want to get technical document of BADi, where can I get it?

Thank you very much!

Wesley