I'm not 100% I understand your question and objectives, but can try to offer some general feedback. If you want better answers with more targeted feedback, I recommend expanding on your description and writing more than two sentences.

An Okta user has a profile of attributes. Of all the available attributes, Okta has four required attributes: username, email, first name, and last name. Of these four attributes, the username must be unique in your Okta org, but you can have several users with the same value for the other attributes.

I've seen some people get confused between the Okta username and the email address. In many other systems, the email address is the username. That is not the case in Okta. They are two separate attributes and users must login to Okta using the Okta username, not the email address. You certainly can make the username and email address attribute the same value. So effectively, the user is logging in with their email address, because it happens to be configured with the same value as the username.

There are several ways to create a user in Okta. You can navigate to Directory > People > Add Person; this method will allow you to manually enter all the require attributes, including the username and email address. The other method is to import the user from another source, like Active Directory or G Suite. When you import a user from another source, there will be options to map the attributes from the source directory/app into Okta. So for example, you can map the UPN in AD to the username in Okta, and you can map the email address attribute in AD to the email address attribute in Okta.

Given you mentioned using a "condition", I suspect the ladder is the method you're using to create users. If that's the case, then simply map the same attribute in the source directory/app to both the username and email in Okta. So for example, map the email address attribute in AD to both the username and email address attribute in Okta. If you later update the email address in AD, it will also update both the username and email in Okta.

If the general feedback above doesn't answer your question, then you might want to provide that more detailed description I suggested. What is the source and target for updating the attributes? What condition/expressions have you tried? Etc.

Not sure if this is what you need, but linked below is the Okta Expression Language:

developer.okta.com/reference/okta_expression_language/