Thank you so much for reaching out to us, I would be happy to assist!
Based on your description, it sounds as if you would like to disable the laptop monitor screen, then set 1 of the external displays as the main monitor or desktop, and then extend to the second external display.
In order to disable the laptop monitor, you will need to open display settings, and then there is a label that says “Multiple Displays” with a drop down box, with the laptop monitor selected, change this drop down box from extended to “Disconnect this display”
In order to have 1 of the external displays connected as “Main” and the other as an extension of the main monitor, you cannot use a Y splitter, as this will only allow you to mirror the displays, and not have them set as two distinct displays.
I hope this information helps, let me know if you have any additional questions.
Thank you for your patience,
Product Owner & Technical Support