Help. Can't figure out the new input system or double jump in general

Help. Can't figure out the new input system or double jump in general. I'm new to coding so would love some help! That would be amazing.

Currently using Starter Assets - Third Person Character Controller from unity asset store https://assetstore.unity.com/packages/essentials/starter-assets-third-person-character-controller-196526

     private void JumpAndGravity()
     {
         if (Grounded)
         {
             // reset the fall timeout timer
             _fallTimeoutDelta = FallTimeout;

             // update animator if using character
             if (_hasAnimator)
             {
                 _animator.SetBool(_animIDJump, false);
                 _animator.SetBool(_animIDFreeFall, false);
             }

             // stop our velocity dropping infinitely when grounded
             if (_verticalVelocity < 0.0f)
             {
                 _verticalVelocity = -2f;
             }

             // Jump
             if (_input.jump && _jumpTimeoutDelta <= 0.0f && _canDoubleJump == false)
             {
                 // the square root of H * -2 * G = how much velocity needed to reach desired height
                 _verticalVelocity = Mathf.Sqrt(JumpHeight * -2f * Gravity);
                 _canDoubleJump = true;
                 _input.jump = true;
                 Debug.Log("jump 1");
                 // update animator if using character
                 if (_hasAnimator)
                 {
                     _animator.SetBool(_animIDJump, true);
                 }

                 else if (_input.jump && _canDoubleJump == true)
                 {
                     _verticalVelocity = Mathf.Sqrt(JumpHeight * -2f * Gravity);
                     _input.jump = false;
                     Debug.Log("jump 2");
                 }
             }

             // jump timeout
             if (_jumpTimeoutDelta >= 0.0f)
             {
                 _jumpTimeoutDelta -= Time.deltaTime;
             }
         }
         else
         {
             // reset the jump timeout timer
             _jumpTimeoutDelta = JumpTimeout;

             // fall timeout
             if (_fallTimeoutDelta >= 0.0f)
             {
                 _fallTimeoutDelta -= Time.deltaTime;
             }
             else
             {
                 // update animator if using character
                 if (_hasAnimator)
                 {
                     _animator.SetBool(_animIDFreeFall, true);
                 }
             }

             // if we are not grounded, do not jump
             _input.jump = false;
         }

         // apply gravity over time if under terminal (multiply by delta time twice to linearly speed up over time)
         if (_verticalVelocity < _terminalVelocity)
         {
             _verticalVelocity += Gravity * Time.deltaTime;
         }
     }