Typically Discord api proposes to send a message to the channel or DMs via BOT(it shows as Bot in the thread). Is there is also possibility to post it using user account via API?
You sound like you are trying to make a self-bot. Let me warn you, that it is against Discord's ToS and you may have your account removed if you get found out.
If you wish to send a message using the API solely without the need of a Bot user, you may find webhooks very useful.