How to transfer chatbot contacts?

Question

Chats

Tell. Now I want to launch a bot(s) chat on some constructor service. In the future, I plan to run bots on my own server. The question is, can I transfer contacts from a third-party service to my database? At the moment, I'm not interested in the question "how to do it" but simply the technical feasibility and complexity of implementation. Are there just some customer identifiers stored there? Do you just need to transfer them?
Interested primarily in Viber and Telegram