So, In order to remove the reset the form you should use the controlled forms. By controlled forms i mean using the states to change form inputs. And that's the recommended way and best practice.

so if you'll have to re-write your your code it'll look something like this.

    import React ,{useState} from 'react';  // import useState hook
    import { Form } from 'react-bootstrap';
    
    const AddItem = () => {
    // Initialise  Values with empty string or null;
    const [inputeVal, setInputVal] = useState({
       carName:"",
       companyName:"",
    });
    
   const handleChange = (event)=>{
   const {name, value} = event.target;
   setInputVal({...inputVal, [name]:value}) // will set the values from input field to relevant state

   }
    
   const handleItemSubmit = () => {
      // your handle submit logic goes here 

     // after submit you can reset the form by resetting the states

     setInputVal({
        carName:"",
        companyName:"",
     })
    
        }
        return (
            <div className='w-50 mx-auto mt-5 py-5 d-block'>
                <Form onSubmit={handleItemSubmit}>
                    <Form.Group className="mb-3" controlId="formBasicCarName">
                        <Form.Control onChange={handleChange} value={inputVal?.carName} name="carName" type="text" placeholder="Enter Car Model Name" />
                    </Form.Group>
    
                    <Form.Group className="mb-3" controlId="formBasicCompany">
                        <Form.Control onChange={handleChange} value={inputVal?.companyName} name="companyName" type="text" placeholder="Enter Company Name" />
                    </Form.Group>
                    <button className='btn btn-primary' variant="primary" type="submit">
                        Submit
                    </button>
                </Form>
            </div>
        );
    };
    
    export default AddItem;

Easy fix is to reset the form like this.

  const handleItemSubmit = (event) => {
    event.preventDefault();
    const carName = event.target.carName.value;
    const companyName = event.target.companyName.value;
    console.log(carName, companyName);
    event.target.carName = "";
    const inputField = document.getElementById("form");
    inputField.reset();
  };

And don't forget to Provide the id to your form

<Form onSubmit={handleItemSubmit} id="form">

However, i will highly suggest you to look into callmeizaz answer above about the useState. Thats the proper way to handle form

reset the form like this:

const handleItemSubmit = (event) => {
     event.preventDefault();
     const carName = event.target.carName.value;
     const companyName = event.target.companyName.value;
     console.log(carName, companyName);
     event.target.reset(); //add this line
}