I'm not 100% certain on what you're looking for, but I have come up with a script that completes what I believe you're asking.

/** @OnlyCurrentDoc */

function getMetric2() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getSheetByName('Sheet1') //change to the name of your sheet

  var uniqueRange = sheet.getRange('A13:A19');
  var uniqueIds = sheet.getRange('A13:A19').getValues(); //change range to the keys in the final output table
  var findKey = sheet.getRange('A3:A5').getValues(); //change range to table 1 unique keys

  var lastKey;

  for(var i = 0; i < uniqueIds.length; i++) {
    //i = row
    for(var j = 0; j < uniqueIds[i].length; j++) {
      if(lastKey == uniqueIds[i][j]) break;
      //j = column
      var trueRow = 13+i; //change constant to the row number that var uniqueIds starts at
      var row = findKey.findIndex(row => row.includes(uniqueIds[i][j]));
      var col = findKey[row].indexOf(uniqueIds[i][j]);
      var foundRow = row+3; //change constant to the row number that var findKey starts at
      
      let metric2 = sheet.getRange('C'+foundRow).getValue();
      sheet.getRange('C'+trueRow).setValue(metric2);
      lastKey = uniqueIds[i][j];
    }
  }
};

This formula iterates through the IDs from the Final Output table, finds them in Table 1, and returns the corresponding Metric2 value for each.

Linked below is the sheet I used to create and test this. Edit permissions are on, and you should be able to click the button to see the script run.

https://docs.google.com/spreadsheets/d/1eJFm5YpL18X5hqZ5tKnHgT5T60dKMSq18bWqibriRqk/edit?usp=sharing

Please let me know if you have any issues with this, or if it wasn't what you were looking for.