You cannot directly retrieve the credentials with a microflow or something else because the password is stored as a Hashed string and it cannot be decrypted (Luckily). What you can do is use the credentials in a "Service", for example via Rest Services.
What you can also do is that you use a System account to log in to an external application, so you do have an integration with an external system, this integration is no longer specific for a certain account, but generic.

You could possibly make your own logic for this with which you also encrypt and decrypt the password yourself, but then we need to know details about the system with which you are trying to integrate. Oh yeah and you have to be very careful with that of course.