Invoke function from Mobile Text Field

I encounter a Mobile Test scenario like this:

When we input the Phone Number which the three first-digit are "628", it will automatically change to "0"

By manual testing, I can do the scenario but I cannot do the scenario with Silk Test ( I am using .NET script)

From the Mobile Text Field, the available methods to input data are SetText and TypeKeys. Both of them did the input of "628" but I failed to make it changes to "0" by the app.

I use Object Locator to check on the object but did not find the function that I can retrieve or invoke.