Start things off by mowing the lawn as this will help with working the top dressing into the grass, later.
Once you’re done mowing, it’s topdressing time.
Spread the topdressing over your turf as evenly as you can. The consistency should be 3-4lb (1.3 - 1.8kg) per sq/yd. Leave it to dry before you start working into the soils as this will make it easier to go down to the base of the sward.
When it’s good and dry, use a landscaper rake(or drag mat or true lute) to work the topdressing into the turf. Repeat this process as many times as necessary, until all of the topdressing becomes part of the soil.
When that is done, let the lawn rest for a few days before you start working on it again. Also if there's no rain during these “few days” lightly water the lawn in order to wash away any loose material.