Hmm, so you have a single record in Table B, and every time a new record gets created in Table A you'd like it to be linked to that one record in Table B?
If so, try:
1. Create an automation that triggers when a new record is created in Table A
2. Give it a "Find Record" action that will look for that single record in Table B
3. Give it a condition logic step
4. If the "Find Record" action's result length is > 0:
- Give it an "Update Record" action that will update the single record in Table B with the value of its linked field to Table A from step 2, followed by a comma and the record ID of the triggering record from step 1 into its linked field to Table A
5. If the "Find Record" action's result length is = 0:
- Give it an "Update Record" action that will update the single record in Table B the record ID of the triggering record from step 1 into its linked field to Table A
And here's a link to a base with that automation set up to get you started!