I can not change the "theme"

Good day!
A user from Russia writes to you. I have a problem :frowning:
I wanted to change the “theme” in the program from gray to black.
And when you press the treasured button “download theme”, it gives such an error.
What is written there -

A program for performing this action is not associated with this file. Install the program or, if it is already installed, create a match using the “Programs by default” control panel component.

<< Этому файлу не сопоставлена программа для выполнения этого действия. Установите программу или, если она уже установлена, создайте сопостовление с помощью компонента панели управления “Программы по умолчанию”. >>

The program was previously installed through the “installer” (purchased from the site and downloaded through it). Now it is installed through STEAM (I thought it would solve the problem), but the error continues to be issued.
Google did not help me in finding a problem, my friends too.
I hope for your help. Thank you in advance!

Yes, also because of this error, the program was not updated. I had to delete it every time and download everything in a new way. (new update - new installation file)