You can use any software development technologies and programming languages that support REST API
Bitrix24 applications TRAINING course
This course overviews key terminology, basic public and local application types, outlines options for REST API app access, as well as introduces applicable examples, including both "Quickstart" and individual third-party solutions integration scenarios aimed at expanding Bitrix24 features.
In this course you can find detailed step-by-step guide on creation and use of Bitrix24 Chat Bot within your Bitrix24 account. It includes instructions on how to implement all the basic Bitrix24 bot and chat functionality: formatting, attachments and commands - all with the goal to enhance your communication capabilities.