The password does not matter.
What precisely did you sell i.e. what drone, what controller and if relevant what phone?
If you sold one of the smart controllers or a dumb controller with a phone or tablet and had not cleared the memory of the old flight logs then the buyer can access all those logs via computer etc..
Similarily, if the controller or phone or tablet was left logged into your account then the buyer has access to the account. HOWEVER, it is my experience that logging out of the account on ANY device that runs the app i.e.
smart controller, phone or tablet, will log you out of the App on ALL 'your' devices as they connect to the internet.
So .... if necessary, instal the app on a phone or tablet etc. then log in and immediately log out and that will 'secure' your account on the
smart controller or phone or tablet.
But they can still access the logs via computer, there is nothing you can do about that unless you can remotely reset the phone or tablet and I would be wary of that if the buyer has used the phone or tablet, ....... you might 'cost' them their own data.
I don't know if remotely resetting a NOT LOST phone or tablet is possible.
If you sold a dumb controller and did NOT include the phone or tablet then your logs are safe.
The next point is vital, YOU MUST unbind
1) the drone from your account and
2) the controller from the drone.
If you do not then the buyer may well get back to you saying the equipment is beep beeped.
You DO NOT need physical access to the drone or controller to do this, all you need to do is log into the account that bound the drone and then, whilst that app is connected to the internet, UNDO the binding of the drone to the account and UNDO the binding of the controller to the drone.
This primarily applies if you had FLYaway insurance on the drone.
If you had neither FLYaway insurance NOR care refresh then I believe the binding you could have established does absolutely nothing to the equipment but, for the buyer's peace of mind, I would still unbind the drone from the account.
If you had neither care refresh nor FLYaway insurance I doubt you were able to bind the controller to the drone.u