Hi jonatan6garcia8x1, welcome to Thunkable! 
Be sure to check out How to ask Great Questions v2.0, the Community Guidelines, and our Getting Started Guide to make the best of your Thunkable Community experience!
For your question, you can search for the value by using dynamic variables. It would look like:
If email_label’s text = cloud variable (join (cloud variable userID) + /Componetes/ + Registro_DNI’s Text) then …
The last thing I would recommend would be to change the way you store cloud variable userID. That cloud variable will store the value of the last person who opened the app on any device. I would recommend using stored variables instead.