What is a border run and how can a Moroccan passport holder do it in Thailand?

Unless you have a multiple entry visa you purchased before you traveled to Thailand, you cannot do a border run. A border run is only to activate a new entry on a multiple entry, or to get a new visa exempt stamp. Your passport is not a visa exempt country, so you cannot get a visa exempt stamp.

You would likely need to make a visa run if you don't have a multiple entry visa. That means you have to go to a Thai embassy or consulate in another country and apply for a new visa.