Ok, Click The Number 2019.4.15f1, after that, go to the 2019 part of the unity websitenext, scroll down until you see the words "Unity 2019.4.15" after that, download it, open it, select the folder named 3.4.5 when you press the add button on unity, and your done!
next, scroll down until you see the words "Unity 2019.4.15" after that, download it, open it, select the folder named 3.4.5 when you press the add button on unity, and your done!