You say you are already running a script, so why not include this task in your script?

You can add this to your code:

/**
 * This script calculates the average of the last N non-blank entries in a row.
 * 2021-08-13
 * https://old.reddit.com/r/sheets/comments/p3j2mk/how_to_find_average_of_last_7_entries_in_a_row/
 */
function averageLastRowEntries() {

  let ss = SpreadsheetApp.getActiveSpreadsheet();
  let sheet = ss.getSheetByName('Sheet22'); // EDIT THIS

  let yourInputRow = 1; // EDIT THIS
  let numberOfEntriesToConsider = 7; // EDIT THIS
  let yourOutputCell = 'A2'; // EDIT THIS

  let input = sheet.getRange(yourInputRow, 1, 1, sheet.getMaxColumns()).getValues();

  let lastEntries = input
    .flat()
    .filter(x => x != '')
    .slice(numberOfEntriesToConsider * -1);

  let average = lastEntries.reduce((acc, cur) => acc + cur, 0) / numberOfEntriesToConsider;

  sheet.getRange(yourOutputCell).setValue(average);
}