IF you haven’t already done so can you read up on template overrides?
A possible solution would be to override tickets.php (the original you might want to base your override on can be found in the wootickets/views directory) and look for the section containing this line:
woocommerce_quantity_input( array( ...
That section ends with this line:
'max_value' => $product->backorders_allowed() ? '' : $product->get_stock_quantity(), ) );
Can you try changing it to:
'max_value' => 1 ) );