<script>
function showSaveButton(){
  AJS.$('button.save-cf-btn').show();
}

function hideSaveButton(){
  AJS.$('button.save-cf-btn').hide();
}
</script>

When you click on "Confirm" a Save button will appear

 

Done with the help of this Javascript

<script>
function showSaveButton(){
  AJS.$('button.save-cf-btn').show();
}

function hideSaveButton(){
  AJS.$('button.save-cf-btn').hide();
}
</script>

 

and 2 field definition rules: 

 

Set on field "confirm" and Condition is set to

confirm:true

 

Another rule

Set on field "confirm" and Condition is set to

confirm:false