2019 Speed Triple Mirrors

The one's I have removed on previous bikes were expanding anchor bolt type inserts. Unscrew and remove the mirror then screw the fastener back into the insert about 6mm then tap the screw with a mallet which should release the insert which can then be pulled out of the bar end.

 

OK, it seems things have changed and there is now some sort of handlebar plug fixed in position. I would suggest you remove the left hand side handlebar grip to see if it is evident how the plug is retained in position. My bike is also a 2019 Speed Triple but I have never removed the bar end mirrors so don't have a definite answer. Note the handlebar grip is retained by 2 screws concealed under the inner end of the rubber grip.

 

@KevinC I am wondering why you just don't put your bar end mirrors on using the existing screws in the bar ends or perhaps using a longer / shorter screw to do the job.