My request method of the form is POST but getting GET in the calling update sql function

I am using flask for my website and want to update an object and when I call the function for the action instead of POST I get the GET request and can't get the execution right this is part of my home.html :

{% for bars in user.barnames  %}
  <li class = "list-group-item">
      <h1 name="barnameId" id="barnameId" >  {{ bars.data }} </h1>
       <form method="post"> 
         <div align="right">
             <a href="/update/{{bars.id}}">
              <input type="button" class = "btn btn-primary" value="update" /></a>  
             <a href="/delete/{{bars.id}}">
              <input type="button" class = "btn btn-primary" value="delete" /></a>
         </div>    
      </form>  
    </li>
{% endfor %} 

this is update.html :

   <p>{{bars.data}}</p>
        <form action="/update/{{bars.id}}" method = "post" >
             <input type="text" name = "sender" id = "sender" class = "form-control" value="{{bars.sender}}">
            <div align = "center">
                <button type = "submit" class = "btn btn-primary" >update</button>   
              </div>
        </form>

this is update function :

@views.route("/update/<int:id>" , methods = ["post" , "get"])
@login_required
def update(id):
    bars = Barname.query.get_or_404(id)
    if request.method == "post" :
        bars.sender= request.form.get("sender")
        try:
            db.session.commit()
            return render_template("home.html" , user = current_user)
        except :
            flash ("something went wrong" , category = "error")
            return render_template("home.html" , user = current_user)
    else :
        flash("method was get" , category = "error") 
        #1
        return render_template("update.html" , user = current_user , bars=bars)

so if I use this I keep getting method was get and go to the update page , if I press the update button in update.html nothing gonna happen and object is unchanged and still the request is GET if I use:

bars.sender= request.form.get("sender")
db.session.commit()

instead of #1 I can update the object but entering the update page I get None as sender (which make sense) ,I can update the object but still the request is GET and also obviously if I go back to home and want to update again I get None as sender so the execution is wrong also if I use :

request.form["sender"]

instead of :

request.form.get("sender")

I get werkzeug.exceptions.BadRequestKeyError: 400 Bad Request

I'm new to coding so sorry if my code and question is dumb