Theme Horse

To make navigation menu center, please go to the Appearance > Customizer > Additional CSS and again paste the below custom css code to the end after the previous code:

@media (min-width: 992px) {
	.navbar-main .container {
		padding-left: 85px;
	}
	.main-navigation {
		width: 100%;
	}
	.main-navigation .navbar-nav {
		display: flex;
		-ms-flex-wrap: wrap;
		flex-wrap: wrap;
		-ms-flex-pack: center;
		justify-content: center;
	} 
	.main-navigation li {
		-ms-flex: 0 0 auto;
		flex: 0 0 auto;
		width: auto;
		max-width: 100%;
		float: none;
	}
	.navbar-nav.d-lg-block {
		display: flex !important;
	}
}

Thanks