Just edit the file with the path: google-calendar-events/includes/class-gce-display.php
And search for this lines
// Add previous / next functionality
//If there are events to display in a previous month, add previous month link
$prev_key = __( ‘Back’, ‘gce’ );
$prev = date( ‘m-Y’, mktime( 0, 0, 0, $month – 1, 1, $year ) );
//If there are events to display in a future month, add next month link
$next_key = __( ‘Next’, ‘gce’ );
$next = date( ‘m-Y’, mktime( 0, 0, 0, $month + 1, 1, $year ) );
