1.Log in to your dashboard--> layout- -> Edit HTML

2.Scroll down to where you see </head> tag.

3.Add below code into your template just above the </head> tag.

#belowheader-wrapper {
width:890px;
margin:0 auto 10px;
overflow: hidden;
}

Note : You can change width:890px to equal the width to your header-wrapper.

4.Now Scroll down to where you see this:

<div id='header-wrapper'>
<b:section class='header' id='header' maxwidgets='1' showaddelement='no'>
<b:widget id='Header1' locked='true' title='Your header title' type='Header'/>
</b:section>
</div>

5.Now paste the below code just after the above code.

<div id='belowheader-wrapper'>
<b:section class='belowheader' id='belowheader' preferred='yes'/>
</div>

6.Click on "Save Templates" and you are done.