how to align featured image to the left of blog post

This CSS:

.ast-single-post-order {
    max-widtH: 50%;
    float: right;
    padding-left: 1em;
}.single .entry-header .ast-single-post-order+.post-thumb img {
    margin-top: 0;
    margin-bottom: 0;
    max-width: 50%;
    float: left;
}

To add or override CSS: use the “Additional CSS” option in the customizer. https://wordpress.org/support/article/appearance-customize-screen/

Learn to use the Chrome Developer Tools or Firefox Developer Tools to help you see and test changes to your CSS.

Do you have any caching optimization plugins or are you using cloudflare? If so, clear those caches.

I don’t see that you put the CSS in at all. I think your best bet is to contact the theme’s developers.