Connect two SharePoint lists

Hi Ghada Mehrez 

Thanks for the additional explanation. If I am understanding you correctly, this should be fairly simple to do. I understand you to say that when an item is created in List A, then a task should be created in Task List B with a link back to the new item in List A, and also the RelatedTo field in that new item should be updated to contain a link to the new task in List B. Is that correct? If so, please see the following flow, which does that using basic actions.

Overview (trigger + 2 actions):

Detail of creating an item in the Task List, including a link to the new item which triggered the flow. You probably already figured out that the name of your task list must be entered manually as it's not listed by default under List Name.

Detail of updating the original item in List A to add a link to the task just created in the Task List. ID and Title are from the trigger item (When item is created), and RelatedTo is the Link to Item from the step just above (Create new item).

Does this do what you want...?

Sandy