They Didn't
Even in in the modern era "surrender" of a combat aircraft in combat isn't a thing. There's just no way to do it (or accept it) safely enough. At best there are accounts of pilots defecting with their aircraft. But that's not really the same thing.
The closest thing to surrender a pilot/aircrew can do is bail out of their machine. The pilot/aircrew are intentionally making it so they are no longer capable of aggressive action. While that in itself isn't a formal surrender, the following rules apply Per Wikipedia:
"In 1977, this practice was finally codified in Protocol I in addition to the 1949 Geneva Conventions:[1]
Article 42 – Occupants of aircraft
- No person parachuting from an aircraft in distress shall be made the object of attack during his descent.
- Upon reaching the ground in territory controlled by an adverse Party, a person who has parachuted from an aircraft in distress shall be given an opportunity to surrender before being made the object of attack, unless it is apparent that he is engaging in a hostile act.
- Airborne troops are not protected by this Article"
This developed after WWI when aircraft became powerful enough for parachutes to be common issue, and from a pilot's perspective a guy who bails out of a perfectly fine aircraft is basically surrendering. But that didn't happen in WWI.
In WWI for a variety of practical reasons (most pilots would rather have more ammo/fuel than a parachute of dubious value) and some official ones (the brits for instance forbade the use of parachutes because they felt it might make pilots bail from otherwise save-able machines) most pilots didn't use parachutes. They were the domain of the observation balloonists, whom pilots as a rule did not like (and frequently shot even when the balloonists were using parachutes!).
With no way to communicate a clear intention to surrender nobody tried it. Remember surrender is a dangerous situation, both for the surrendered (who needs must put themselves in the power of people trying to kill them) and the person taking the surrender (who must worry about it being a trick or exposing himself to the danger in other ways to accept the surrender). People in general would rather run than surrender, and the more dangerous surrender seems, the more likely they are to run. Even in situations like aerial combat where you might literally be incapable of escaping due to flying an inferior machine.