Anne has made a few tutorials on how to add field names to OpenStreetMap.
To follow the first video, all you need is your knowledge of fieldnames, a computer with an internet connection and a browser like Firefox or Chrome.
The next two videos are two parts of one tutorial which uses FieldPapers (see under Tools). You will need a scanner or a digital camera for this method of adding field names. It is more convenient for group work or during lockdown, when you cannot visit the informant.
If you are dealing with old fieldnames, where the fields have since been merged into one large one and you are trying to find the old field boundaries, this tutorial using the British War Office map might be helpful: