This problem may be complicated since you have 2 different definitions of x. However, based on what you asked for, this should work.
The upper signal is passed through whenever f1(x) is greater than -0.1. If f1(x) <= -0.1, the lower signal is passed through.
Note that the switch will always use the value of f1(x) to determine which value to pass.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/211707/image.jpeg)