Hi @rampprakash
Thank you very much for your guidance. So I have choose my entity (which is the parent) from the screen you're showing, and then press OK.
It will bring me to another screen, which is the process it self.
1. Choose the Scope : Organization
2. Start when : After, and then choose "Record fields change" and select the field I wanted.
3. In the process below : Add Step, bring to another screen.
4. Choose Check condition and setup the condition whereby I need to check if the field on the parent table (Posted) = Yes
5. Save and Close
6. Click the new row and Add Step and choose Update.
At this point, in the dropdown selection, I cannot find the child table which I set the relation already.

Isn't in this drop down supposed to showing me my child entity / table ?
Many thanks in advance for your help.