Hi @Maria_Juliana_Yepes !
So you have on record in Table B, which shall be linked to all records getting added in Table A.
This is possible with automations, but you’ll have to overcome the issue of overwriting the linked record field in Table B instead of adding to it.
The trigger for the automation:

The firs action step is the a “Find records” step, in which you search for the record in Table B (in order to know which records are already linked). You will have to create a field containing the record id first (formula field and the formula is simply RECORD_ID()
). Then you use the record id of the single record in Table B to actually find that record in the action step:

The last step is then to update the record in Table B:

The trick here is to use the previous values of the linked field in Table B (which you’ll find from the “Find Records” step) and add the new record id (from the record that got created, step 1):

Let me know if you run into any issues setting this up