In order to delete a row from repeater ACF using PHP, you have to open functions.php and use the following code.

In the below example $repeater_key is the key of the element that was clicked. You have to check if the keys start from 0, if they do, you will have to increment it by 1.

$repeater_key = (int)$_POST['key'];
delete_row('field_615c0bb5ceb1d', $repeater_key, $post_id);

If you want to delete a row from the user group, you will have to change the code like the following:

delete_row('field_615c0bb5ceb1d', $repeater_key, 'user_'.$post_id);

Also if you want to delete a row from the taxonomy group, your code should look like something like that:

delete_row('field_615c0bb5ceb1d', $repeater_key, 'term_'.$post_id);