I was just wondering if sitting US presidents can repeal their own executive order?
For example, a president issued an executive order (forget the content). Can the same president revoke that executive order say after 2 days?
Its helpful to think of Executive Orders as similar to directives issued by the CEO of a company. CEO's aren't supposed to issue orders that are contrary to the law and often the directives are at a relatively high level (i.e. lots of details are to be determined). An example, the CEO says "let's reorganize the company by March 31 to better serve our customers". She might have an idea about who is going to lead that effort, but doesn't explicitly spell out every new role, title, responsibility, etc. Others will do that.
A year later, the CEO could decide the reorganization isn't working and issue a directive to do something completely different.
Similarly Executive Orders aren't creating new laws. Even Trump's first week Executive Order to build the wall at the US/Mexican border was mostly "directional". Under a 2006 law that authorized 700 miles of barrier, only 649 had been built. So in part the order said, build the remaining 51miles (already a law) and then start planning for an additional amount of wall (no law is required to start a planning process). Next month he could just as easily issue an order saying "defer plans to build additional wall until I say so" (or issue another Executive Order).
This article seemed to do a pretty good job of explaining things.
A president can issue an executive order on any subject at any time. If the executive order replaces a previous order, then the previous order has been "repealed". A trivial example would be congress passes a law to create a seal for an agency, the president (under that law) says the background would be green. Sometime later, he issues a new order that the background would be red. The previous order has been "repealed".
A sitting US president can repeal any executive order, theirs or their predecessors.
An executive order can cover any matter. This would include the repeal of previous executive orders (theirs or otherwise).