Updating a table when a new record is added

I’m a new AIRTABLE user and I can’t manage to set up my first automation.
I have a USER table and a TODO table
As part of an onboarding process, when I add a new user, I want all the tasks in the TODO table to be assigned to that user.
My attempts have been unsuccessful… can you help me?
See attachment
Thank you for your help

Is your list of todos static or chancing all the time?

If it is static, maybe having the automation in your USER table to fill in a linked field in USER table. That field will be linked to all your todos in TODO table.

That’s one way. If your list of todos changes all the time, it becomes more tricky, in that case I would do a rollup to get array from all linked records in TODO table and then try to separate them so that I fill in with the automation.

If your Todo’s are changing, here comes the next question, for the existing users, should the list of todos be updated or not?

Hello and thank you for your feedback.
The table must be updated dynamically, yes, and for all users, even existing ones.
I think I’ve found the solution by looking around.
I’ve added a check box column which will trigger an automation as described here:

I’ll keep you posted as it also has to work both ways (USER update when I add a new task).

Hello and thank you for your reply.
I’ve finally found the solution to my problem with merge tables… the initial construction of my table was poor… Thanks again