Slack-bot - how to add an add file button?

Question

Bots

Hello.
Please tell me how to be?
We want to use it to support the bot in slack, but we ran into a problem with attaching a file.
Block Kit Builder simply does not have such a "button".
Has anyone found a way to solve this?
the bot is called through the command / , and not through @
in dialog mode, yes, this can be done, but through the form we can’t figure out how.
thank.