Custom Width for Any Specific Post/Page

So here is something weird (or maybe interesting) I want to do.

Here is the blog post I want to change.

How To Start a Blog in 2019 That Makes Money on Autopilot

I have found one CSS code to change the width of the full-width page.

.no-sidebar:not(.generate-sections-enabled) .site.grid-container,  .generate-sections-enabled:not(.home) .generate-sections-inside-container {
    max-width: 950px !important;
}

.one-container .site-content {padding:40px 20px}

But I want to make ONLY THIS post as per the width specified by this code.

I have found one solution for this too.

In the Hooks, I will create one hook with the code (I don't know what that code will be) and make that hook be active on a specific TAG only.

So by doing this, when I select that specific tag for any post, it will automatically take that layout.

Now help me to write the code which can do this for me.

and let me know in which hook I should add that code.