Hi @Mr.Sai - first of all, I highly recommend you start managing your apps from developer.twitter.com (rather than use apps.twitter.com). You should also apply for a developer account, which will allow you to create new apps if you desire to do so going forward.
Although you can currently still manage existing apps on apps.twitter.com, we will soon retire this site and consolidate all developer tools, API access, and app management within the developer portal at developer.twitter.com.
Your developer account (where you manage your apps for access to Twitter APIs) is linked to your Twitter account. Changing your login details on Twitter is not expected to have an impact on your app keys and tokens.