Hi Teodora,
I understand that you are facing an issue while completing the 'Design Filter with Cutoff Frequencies' Task 1 in 'Signal Processing with MATLAB' Course.
The Task states to change the sample rate of the variable designedFilter. However, in the dialogue box of Design Filter, the parameters are set for the variable designedFilter2 as shown by this image:
To resolve the issue, please edit the variable name from designedFilter2 to designedFilter as given by this image:
I hope this helps!