Farmers told to cut Milk production

In Scotland the dairy Farmers have been told to cut Milk production. How do they do that go into the fields and ask the Cows to not produce as much. Read below from the BBC news website.

The dairy manufacturer Muller has ordered farmers across Scotland who supply them with milk to cut production because of an oversupply.

It has written to more than 250 dairy farmers asking them to reduce output because of changing consumer habits caused by the coronavirus crisis.
It has been estimated more than a million litres of unwanted milk is being produced across the UK each day.
This means some dairy product is having to be poured down the drain.
Even though demand from supermarkets has increased, that has not filled the gap left by the closure of cafes and restaurants.