The button is not in "table 1", but in a given record of that table. The field to be modified is not in "table 2", but also in a specific record of that table. It is very difficult to suggest anything without knowing what kind of relation exists between those two records. Please add some more information...

for t in select Table2 do
  if t.Formula = "Yes" then
    t.('Yes / No' := true)
  end
end

for t in select Artists do
  if t.'before today' = true then
    t.('artist paid' := true)
  end
end

If the "artist paid" and "before today" fields are of type "Yes / No" then the above may work. I have not tested it.

I just tested it and it works. As I mentioned above, the 'before today' and 'artist paid' fields must be of type "Yes / No" in order for the code to work. Go to the Actions tools pulldown menu and select "Edit fields". There you will see the various field types listed. Drag the "Yes / No" type fields from right to left. Hope this helps.

From what I understand of the structure of your database, in the "Artists" table, there should be a field called (by default) "Events", which is a "Reference from Artists to Events 1:n". This field was created automatically when, in the "Events" table, you created the reference to the "Artists" table.

If this is correct, the following script should do what you need:

for e in Events do
if e.'before today' then
e.('artist paid' := true)
end
end

Add a button in the "Artists" table, and paste the above code in the "On click" field. Set the name of the button to, of course, "Artist paid".

Just for the record, an even simpler  script:

for e in Events['before today'] do
e.('artist paid' := true)
end

Ockam's razor is still sharp. Would you believe that this single-liner does the job:

Events['before today'].('artist paid' := true)

Alain, this one line of code is very powerful. Thank you for sharing it.