How to link primary text frames in existing documents

You did not specify script language. Here is a simple script written in AppleScript that connects text frames in a document in the order in which they were created. This works using the id of the text frames. You will want to make sure the text frame ids are returned in the correct order (depends on preference settings). The variable at the end of the script (frameList) will allow you to verify the ids of the text frames. If the numbers are in the correct order, remove the (*  and *) and run the script again to link the frames.

set frameList to {}

tell application "Adobe InDesign CC 2019"

  tell document 1

  repeat with i from 1 to count (spreads)

  set pageList to (id of every text frame of spread i)

  set revList to reverse of pageList

  set frameList to frameList & revList

  end repeat

(*set thisFrame to text frame id (item 1 of frameList)

  set numLinks to (length of frameList) - 1

  repeat with i from 1 to numLinks

  set nextFrame to text frame id (item (i + 1) of frameList)

  set next text frame of thisFrame to nextFrame

  set thisFrame to nextFrame

  end repeat*)

  end tell

end tell

frameList

No, it is not working. There si no scripts for indesign.