How to Hide Doneren met Mollie Admin Menus

function plt_hide_doneren_met_mollie_menus() {
	//Hide the "Donations" menu.
	remove_menu_page('doneren-met-mollie');
	//Hide the "Donations → Donations" menu.
	remove_submenu_page('doneren-met-mollie', 'doneren-met-mollie');
	//Hide the "Donations → Settings" menu.
	remove_submenu_page('doneren-met-mollie', 'doneren-met-mollie-instellingen');
}

add_action('admin_menu', 'plt_hide_doneren_met_mollie_menus', 11);

Where do I put this code?