It would seem that you have a many to many relationship between Observations and DataPoints with a table named ObservationsDatapoints set up as the join table.
I think you need to create records in that join table that correclty link observations and datapoints to each other.
That's what I thought I explained in my post. Maybe I didn't. I need to populate those fields but match datapoints and observations together based on specific matching conditions from the original data. I typed out what those conditions are, but I don't have any idea how to express this in FileMaker.
Your original post made no mention of a Join table so I was checking to make sure you understood that was what was needed. Especially since you are NOT matching observations to Datapoints in a parent child relaitonship.
And I found your "where" statement confusing. Can you post an example of the actual data? Just a few rows of data with the columns identified should be sufficient to enable someone to suggest a script that can loop through your imported data and populate the needed records.