Activate submit button on form change and detach event listener
If you use event.currentTarget instead of form, you can declare the event handler function once and reuse it:

function formHandlerChange(event) {
    const form = event.currentTarget;
    const submit = form.querySelector('.disabled');
    submit.classList.remove('disabled');
    form.removeEventListener('change', formHandlerChange);
}

for (const form of document.querySelectorAll('form')) {
    form.addEventListener('change', formHandlerChange);
}


(Note: I also used querySelector() and querySelectorAll() as they are more flexible than the various getElementBy methods)