The Events Calendar: Event Aggregator: Override import range default.

functions.php

<?php
/**
 * The Events Calendar: Event Aggregator: Override import range default.
 *
 * @see  Tribe__Events__Aggregator__Settings::get_import_range_default()
 *
 * @link https://gist.github.com/cliffordp/6090c1051c82130f093bfcb2b60621d5
 * @link https://theeventscalendar.com/support/forums/topic/is-there-a-way-to-import-events-up-to-12-months-in-the-future-instead-of-three/
 */
add_filter( 'tribe_aggregator_import_range_default', 'cliff_ea_import_range_one_year' );
function cliff_ea_import_range_one_year() {
	return YEAR_IN_SECONDS;
}