JSFiddle - React, Tailwind, and code Playground

HTML

<select class="form-control" name='grupo' id='grupo' onChange="modifica()">
   <option value='0'>Seleccione Planilla...</option>
     <option value='1'>1</option>
     <option value='2'>2</option>
</select>

<form name="imprimir" action="" method="POST">
	<input type="text" id="id_grupo" name="id_grupo" value="">
	<input type="text" id="name_grupo" name="id_grupo" >
	<input type="submit" class="btn btn-danger" value="IMPRIMIR">
</form>

JavaScript

function modifica(){
document.getElementById("id_grupo").value = document.getElementById("grupo").value;      
		}