Bootstrap navbar positioning - html

Question

I'm fairly new to bootstrap so don't really understand all the classes. I've been trying to play around with them for the past day or add my own new ones to get this to work but its no use.
Basically in the following index page I have an input field and search/submit button beside it. The search button however goes under the input, and I wish for it to be beside it. Anyone help?
<!-- Navigation -->
<nav class="navbar fixed-top navbar-expand-lg navbar-dark bg-dark fixed-top">
<div class="container">
<a class="navbar-brand" href="index.php">L'amour</a>
<button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse" data-target="#navbarResponsive" aria-controls="navbarResponsive" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarResponsive">
<ul class="navbar-nav">
<li class="nav-item float-left">
<a class="nav-link float-left" href="order.php">Contact Us</a>
</li>
<li class="nav-item float-left">
<a class="nav-link float-left" href="testimonials.php">Testimonial</a>
</li>
<li class="nav-item float-left">
<form method="post">
<div class="form-group">
<input class="form-control" type="text" name="search" placeholder="Search for wedding...">
<input method="post" name="submit" class="btn w_search form-control" type="submit" value="submit" >
</div>
</form>
<li>
</ul>
<ul class="navbar-nav ml-auto">
<li class="nav-item ">
<a class="nav-link" href="order.php">Order Wesbite</a>
</li>
<li class="nav-item dropdown">
<a class="nav-link dropdown-toggle" href="#" id="navbarDropdownBlog" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
Account
</a>
<div class="dropdown-menu dropdown-menu-right" aria-labelledby="navbarDropdownBlog">
<a class="dropdown-item" href="signIn.php">Login</a>
<a class="dropdown-item" href="sign-up">Sign up</a>
<a class="dropdown-item" href="homeUser.php">Account details</a>
<a class="dropdown-item" href="logout.php">Logout</a>
</div>
</li>
</ul>
</div>
</div>
</nav>

Answer 1

A form example is shown in the Navbar documentation...
https://www.codeply.com/go/dFcxxvzjly
<li class="nav-item">
<form method="post" class="form-inline">
<input class="form-control" type="text" name="search" placeholder="Search for wedding...">
<input method="post" name="submit" class="btn w_search form-control" type="submit" value="submit">
</form>
</li>