syft 0.2.9 requires torch~=1.4.0, but you have torch 1.7.1 which is incompatible. syft 0.2.9 requires torchvision~=0.5.0, but you have torchvision 0.8.2 which is incompatible. code example

Example: ERROR: Could not find a version that satisfies the requirement torch===1.4.0

The most likely reason is a 32-bit installation of python, while 
the torch libraries rely on having a 64-bit version. 
Just start python from command line and observe

C:\Users\user>python
Python 3.7.4 (tags/v3.7.4:e09359112e, Jul  8 2019, 20:34:20) 
[MSC v.1916 64 bit (AMD64)] on win32

If it shows 32, then install 64-bit python