Whether it's an established lawn or a newly seeded lawn. If it's got creeping grasses in the seed, it can be thickened up with ease. All it needs is a little time and to follow these steps.

In this video I apply a quarter rate high Nitrogen fertiliser (46-0-0) - any will do. This one will be fine https://amzn.to/3XkfeSL

I also apply some seaweed (Multi-mite - https://amzn.to/3XjFYmw)

I also apply some Emerald Green (my own product - https://lawnright.co.uk/product/emera...)
Then water it in..

Finally mowing almost daily!