Hi there!
Please take my apology for the delayed response.
You will find a login module in your Joomla backend, login/logout redirection links can be assigned there as per your need.
https://prnt.sc/VMltyGNbSOjq
https://prnt.sc/DZb0E0-EaFVD
If you want to change the image of the modul login then you can use the following code as sample and put in your custom CSS:
.sp-custom-login #login .login-bg-img {
background-image: url(../images/login-image.png);
}
Please use your own image link from the media in the above code.
Note: Path towards custom CSS(Joomla 3): Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.
Best Regards