Edit Wordpress Plugin

General information for the website: Salon Num. of web pages/modules: 0 Description of every page/module: We have salon booking system using following plugin. we need small modification on it https://wordpress.org/plugins/salon-booking-system/ Description of requirements/features: We need to adding Fix amount Service charge to total invoice. at the moment it does not have that option. after this it connected strip payment gateway. we need to charge correct amount very well. better check our attached image Extra services needed: Customization, Other Specific technologies required: wordpress plugin Extra notes: