CVX ,can't be installed by using matlab

I had tried to installed the cvx by using matlab like this video: https://www.youtube.com/watch?v=CmskN_RzAf4,However, after i write the cvx_setup and enter,the window showed " Undefined variable “cvx_setup” or function “cvx_setup.m”. " i don’t know how to solve this problem, i also tried to find the solution on the internet,but it seems that there is no one who has this installed problem like me

Within MATLAB, did you direct to the folder (as shown in the address bar in MATLAB) containing cvx_sestup? You need to do that before issuing the cvx_setup command.

yes i did,but the file be downloaded automatically in D:/ instead of C:/

Put the cvx folder somewhere. Then navigate to that folder (directory) in the MATLAB address bar. Then issue the command
cvx_setup