Remove access for user from multiple files on Google Drive - https://blog.tomtasche.at/2018/02/remove-user-from-multiple-documents.html

appsscript.js

function main() {
  findSharedDocuments("tomtasche@gmail.com");
}

function findSharedDocuments(email) {
  var files = DriveApp.searchFiles('("' + email + '" in readers OR "' + email + '" in writers) AND NOT ("' + email + '" in owners)');
  var success = 0;
  while (files.hasNext()) {
    var file = files.next();
    try {
      file.revokePermissions(email);
      success++;
    } catch (e) {}
    
    Logger.log("file: " + file.getName());
    Logger.log("success: " + success);
  }
  
  var files = DriveApp.searchFolders('("' + email + '" in readers OR "' + email + '" in writers) AND NOT ("' + email + '" in owners)');
  var success = 0;
  while (files.hasNext()) {
    var file = files.next();
    try {
      file.revokePermissions(email);
      success++;
    } catch (e) {}
    
    Logger.log("file: " + file.getName());
    Logger.log("success: " + success);
  }
}

function findOwnedDocuments(email) {
  var files = DriveApp.searchFiles('"' + email + '" in owners');
  while (files.hasNext()) {
    var file = files.next();
    Logger.log(file.getName());
  }
}