There are a app that sync child to parent. 
If you like to build it your self you need to do it using API. 

You need to 2 web request nodes, one to get the parent ticket and the second to update the parent ticket. 

/api/v2/tickets/cid]?include=related_tickets

With that you get the parent ticket ID, then https://api.freshservice.com/v2/#update_ticket_priority to update the ticket. 

@Daniel Söderlund, thank you for the reply.  In my workflow, I have the child ticket created and mark the parent as pending.  Would I be able to continue in the same workflow and adda  conditional of when child ticket is closed, to change status for parent at open?  I know a WF cannot kick off from another workflow change, so not sure how to kick off this aspect of changing status on the parent when the child is closed.  I understand using the API, but cannot see how to kick it off.

You need a separate workflow for the child ticket.  To skip one web requests in that you could add the parent ticket number in a custom field. 

@Daniel Söderlund i cannot get the API to get the parent ticket.  I created a custom field to try to put the parent ticket in, but still doesn’t put the parent ticket in.  Seems the field for parent ticket is mysterious and does not work.  Any ideas?  

I did open a ticket with Support to get their help as well.​​​​​​

Hello, 
I am trying to do similar things;

I want if the parent status is change to update child ticket with the same status,
I can see in automation an event “if status is changed from “ i put Any to Anye;
i added an action on child tickets but i am not able to get the parent status to make the update.
Any help is appreciated
 

@MeriemNAIM Working with FS support, I was able to get it working.  I had to create another WF that had the event based on status is changed from any to resolved.  Then the conditional that would only include the child ticket (I created a custom field that the other WF checked a box and this was the conditional).  Then a web request to get the parent number, the a Parse action, then a web request to update the parent.  it works great.

I would be happy to jump on a call with you to talk through it if that is helpful.  

​@shannon.mejia Would you be available to join a screenshare with me to walk me through your setup. We have a similar workflow - resolved child → resolved parent status. I’m trying to automate and it seems you got this workflow setup and working? Any help would be much appreciated!!

​@Rae for sure, I would be happy to chat with you on this.  Send me a DM and we can set something up.

Shannon

One thing to hit on - I know that you ended up going the API route, but ​@Daniel Söderlund also mentioned the app “Parent-Child Synchronization” in his initial post. I use this app and it has really been very nice to keep that relationship between the child and parent tickets synchronized along with all of the posts that occur.

One option is closing the parent ticket automatically when all of the child tickets are closed. While I have it disabled, it is an option that I tested and it works as advertised.

If you want to check out the app, you can find it here: https://YourFreshServiceURL/a/admin/marketplace/gallery?route=app&id=12097

** Make sure to replace YourFreshServiceURL **

I found a way you don’t need the first webrequest to get the parent ticket ID. 

Don’t know if this is a but but you can use {{ticket.predecessor_ticket.id_numeric}} to get the parent ticket ID.

You can get most fields from the parent ticket by adding “ticket.predecessor_” to the placeholder. 

Like this 

Current ticket 

{{ticket.agent.name}}

Parent ticket 

{{ticket.predecessor_ticket.agent.name}}

But you still need to use API/webrequest to update the parent ticket.