Request Password Change (PHP+MYSQL)

Hello i have this form and my php code skills not very good if someone make change password I would be glad thank you

<div class="col-lg-9">
                <div class="nk-box-3 bg-dark-1">
                    <form class="change-password" method="post" action="">
                        <input type="password" class="form-control input-change-password" name="opass" id="opass" placeholder="Old Password">
                        <div class="nk-gap-1"></div>
                        <input type="password" class="form-control input-change-password" name="npass" id="npass" placeholder="New Password">
                        <div class="nk-gap-1"></div>
                        <input type="password" class="form-control input-change-password" name="cnpass" id="cnpass" placeholder="Repeat New Password">
                        <div class="nk-gap-1"></div>                        
                        <button type="Update" class="nk-btn link-effect-4 ready"><span class="link-effect-inner"><span class="link-effect-l"><span>Change password</span></span><span class="link-effect-r"><span>Change password</span></span><span class="link-effect-shade"><span>Change password</span></span></span></button>
                    </form>
                </div>
            </div>