html,body{
      height: 100%;
    }
    
    
      <div class="container h-100">
    <div class="row h-100 justify-content-center align-items-center">
      <form class="col-6">
        <div class="card"><div class="my-2 mx-2">
          <div class="form-group">
            <label for="formGroupExampleInput">Example label</label>
            <input type="text" class="form-control" id="formGroupExampleInput" placeholder="Example input">
          </div>
          <div class="form-group">
            <label for="formGroupExampleInput2">Another label</label>
            <input type="text" class="form-control" id="formGroupExampleInput2" placeholder="Another input">
          </div>
          <div class="form-group">
            <label for="formGroupExampleInput2">Another label</label>
            <input type="text" class="form-control" id="formGroupExampleInput2" placeholder="Another input">
          </div>
          <div class="form-group">
            <label for="formGroupExampleInput2">Another label</label>
            <input type="text" class="form-control" id="formGroupExampleInput2" placeholder="Another input">
          </div>
        </div>
      </div>
    </form>   
  </div>  
</div>

Çözümü budlum kendim cevaplayayım işe yarar belki.

https://www.codeply.com/go/raCutAGHre