One of the little known secrets of Google's online labyrinth of sites is passwords.google.com, a destination where you can view, copy, and delete all the passwords you've agreed to save with Google and/or Chrome. For a while, the site didn't let you edit saved passwords, but now it does. And that same functionality can be accessed inside Chrome on Android and desktop (and possibly other platforms too), but it requires a trick now. Soon though, it'll be implemented natively.
When you changed an online login that you had previously saved with Google (be it natively on Android or through Chrome), the only recourse to edit it used to be to delete it first, visit the website or app again, enter your new details, and agree to have Google save them. No other password manager worth its salt would make you go through that hoop, so it's nice to see Google fixing this.
First, the passwords.google.com page now offers an edit option for all saved logins. So you can change your username and/or password. But you may often forget to access that site, and even when you do, Google usually asks you to log in again (including 2FA if it's enabled) to verify your identity.
To make the process a little easier, I suggest you choose that site to be your default password manager in Chrome. Head over to chrome://flags/#google-password-manager (copy the URL and paste it) be it on Android or desktop, enable the flag, then reboot Chrome. When it's done, go to Chrome's settings, look for Passwords, and the new UI will be loaded instead of Chrome's native one. There, you can view, copy, delete, and edit any login detail you've saved with Google.
Compared to Chrome's original password interface, this UI gives you broader control, including editing. And compared to manually opening the Passwords website, you get faster verification using only your phone's PIN or fingerprint.
If you don't want to tinker with Chrome flags, there's still more hope on the horizon. According to a Chromium bug tracker issue discovered by 9to5Google, the Chrome team is working on adding this natively in Chrome's own password manager. The request has been pending since 2014, but it's now been assigned and will be coming to Android first, possibly followed by desktop.
When it's live, it'll be under the chrome://flags/#password-editing-android flag. It'll probably show up for Canary first, then make its way down to the stable channel. We'll keep an eye open and let you know when that happens.