If I am not mistaken, you just need to locate the widget file:
/wp-content/plugins/woocommerce/includes/widgets/class-wc-widget-price-filter.php
Then look for this line below:
<button type="submit" class="button">' . __( 'Filter', 'woocommerce' ) . '</button>
Then change the ‘Filter’ to something else would do.
Please let me know if this doesn’t work, I haven’t really try it before.
Best of luck.