If you have forgot the wordpress login URL because you renamed it using a plugin, such as rename-wp-login, then you can resolve the issue by changing the login URL back to default for the time being.

First you will need to SSH into your server, and then move the plugin directory with the _ character to disable it. This works on all plugins. Just remember after you move the plugin directory in order to get access to the wp-login.php URL you need to clear your browsers cache, which is ctrl + shift + delete in chrome.

After you have moved the plugin, and cleared your cache the login url should work on the default wp-login.php

Now I would recommend renaming the plugin back to its default name, re-activating the plugin, and updating the login URL again. This is important because it will prevent most bots from accessing your login page, and trying to login, which is a very common vector of attack for wordpress sites.

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Here is a video guide as well: https://www.youtube.com/watch?v=nivw9Z73Ljs