I believe by default it is the End button, which is not too difficult to find by touch… find the arrow keys which are quite distinctive to feel. Move you hand directly forward and you can feel the insert key which is in the middle of three buttons… go to the left key then the end button is behind that.
However, I suggest you check out VoiceAttack which is ideal for this kind of thing in VR… basically uses speech recognition so you can say key words or phrases that Voice attack then sends the corresponding keyboard button… e.g, you could set it to recognise the phrase ‘toggle drone’ and it would tell MSFS you has pressed the end key. 