Hi Brianna,
It seems that the path directory is not correct. Replace 13.1 with 20.1 in the path directory like so: "C:/altera/20.1/modelsim_ase/win32aloem/".
Make sure the path directory is correct; change it according to your installation directory path. You can check your computer for this. It might be under "C:/intelFPGA_lite/20.1/modelsim_ase/win32aloem/", and if so, change your path directory on Quartus following the aforementioned address.
If your issue isn't resolved, make sure your ModelSim is selected in your EDA settings. To do this, go to Assignments>Settings>EDA Tool Settings>Simulation and make sure you have ModelSim selected under tool name.
Note: If both ModelSim and ModelSim-Altera are available it would select ModelSim-Altera by default. You may need to repeat this process every time you open Quartus again depending on your OS.
Regards,
Nurina