Automation for update of Link to another record field

Hey guys,
How can I update the ‘link to another record field’ (that has allowed linking to multiple records) via automation?
I got to the point where everything works fine until I have multiple records to connect with that “Link to another record” field. It just keeps replacing the previous file, instead of stacking them together.

How ti should look

image

But instead it’s basically infinite loop of one record replacing the another one and so on…So I always end up with only one record connected.
image

EDIT: Forgot to say, trigger is a checkbox field.

You need to include the previous values in the list you send to update. Separate the items with a comma. If there might not be an existing list you may need to use conditional actions so that you can only include the comma when there is an existing list.