Using the In-Editor method

1. Launch Unreal, then open the Project Settings dialog through the Edit menu:

2. Under the Engine - User Interface section, there is a curve called the DPI Curve, which can be used to alter the UI scaling factor based on the short dimension of your screen:

3. Click on the second dot, or keypoint, on the graph.
4. Change its Scale value to 1. Then, do the same for the first dot and set its Scale value to 1 as well:

5. Return to the main editor and run the game again. You should notice that the button is larger than it was before:

Easier to see button on the game screen