So there are several ways, you simply need to let Construct know how to identify which one you want.
The perfect way would be through its UID (Unique ID), which is different even for copied texts (or sprites). You can find it on the left bar.
All you need to do is: Go to the text object's condition -> Pick by UID, and then make a sub-event for its action, e.g.: 'Set Text: Hey I'm so unique!'
But 'picking' could be done through many ways, e.g:
1) its opacity
2) its position (nearest to something?)
3) its instance variable
4) its Z level, top/bottom
5) ..or any expression or evaluation you can think to differentiate them*
* Go to System: Pick object by: (here you can see many options, most relevant for you is Pick by Comparison).