Currently, there is no file upload functionality in the einstein chatbot – between Bot and a Customer. A file transfer facility is available between Agent and Customer, by transferring chat from Einstein bot to Agent and then Agent can request the customer to transfer file by sending a link to transfer file.
A customer can’t upload a file until you initiate the file transfer by clicking the file transfer icon. This restriction helps prevent customers from uploading unsolicited or potentially dangerous files into the chat.
The is an idea to allow file transfer through Einstein BOT: https://trailblazer.salesforce.com/ideaView?id=0873A0000015BDVQA2