Modify Docflow value

Hello experts,

I am reading one opportunity and in that i have one doc flow,

so i am trying to modify the value of field Logsys_a,for this i am using 'CRM_DOC_FLOW_MAINTAIN_OW'  fm.

But still value is not getting modified.

Please let me know how can i modify this value.

Thanks & Best Regards,

Nikhil Haldankar