Hello ! I'm Aymeric, and I'm here to help !
Open the Microsoft Edge settings by clicking on the three dots at the top-right corner of your screen. Choose "Settings".
On the left side of the window, click on "Start, home, and new tabs". There's a section called "When Microsoft Edge starts" : here, you will be able to select Edge's behaviour at start-up.
Feel free to ask if you have any other question !