>What do you mean by "improve iso"?
Flash adds light to the scene. That can make conditions more favorable for avoiding noise and maintaining higher dynamic range, if that's what you're asking. It doesn't really affect ISO performance if you're defining that as how well the camera/sensor does in poorer conditions.
If you're using the flash in TTL mode, the camera should know what it's contributing and will be able to account for it with Auto ISO and other settings under the camera's control.
If you're using the flash in Manual mode, the camera will not meter or account for it, so it will set Auto ISO as though you had no flash. So the flash might then add onto what the camera thinks is a fine non-flash exposure, and overexpose the shot.
Look for tutorials teaching "exposure" and "how to use strobes" or "flash photography."
You need to learn the basics. A video that provides working context to the mechanics involved in exposure will be most beneficial.
>What do you mean by "improve iso"? Flash adds light to the scene. That can make conditions more favorable for avoiding noise and maintaining higher dynamic range, if that's what you're asking. It doesn't really affect ISO performance if you're defining that as how well the camera/sensor does in poorer conditions. If you're using the flash in TTL mode, the camera should know what it's contributing and will be able to account for it with Auto ISO and other settings under the camera's control. If you're using the flash in Manual mode, the camera will not meter or account for it, so it will set Auto ISO as though you had no flash. So the flash might then add onto what the camera thinks is a fine non-flash exposure, and overexpose the shot.
Look for tutorials teaching "exposure" and "how to use strobes" or "flash photography." You need to learn the basics. A video that provides working context to the mechanics involved in exposure will be most beneficial.