Autofill checkbox using string query in url but specifying a fieldset

I'm trying to get filtered data from a webform more quickly. Basically I want to use URL input to specify a date and to precheck a checkbox. I'm getting stuck with how to specify the check box as I'm not sure what the value should be.

<form action="/xxx/yyy" class="form-inline d-flex justify-content-end" method="get">      <div class="input-group input-group-lg mb-2">
        <div class="input-group-prepend">
          <span class="input-group-text"><i class="fa fa-calendar"></i></span>
        </div>
        <input type="text" name="from" value="" class="form-control datetimepicker-input" id="datetimepicker7" data-toggle="datetimepicker" data-target="#datetimepicker7" autocomplete="false">
        <div class="input-group-append">
          <button type="submit" class="btn btn-dark"><i class="fas fa-arrow-right"></i></button>
        </div>
      </div>
</form>

####snip and skip to the part of the form I wish to pre-check####

<fieldset id="departureGatewayFilters">
            <div class="form-check">
              <input class="form-check-input" type="checkbox" value="AMS" id="departureGatewayCheck_AMS">
              <label class="form-check-label" for="departureGatewayCheck_AMS">
                AMS
              </label>
            </div>

So far I'm using URL string: /xxx/yyy?from=2020-03-05 - what would I need next to pre-check the checkbox as well?

Thanks in advance!

Clare