How to test for specific players at specific locations with command blocks
/testfor @a[x=X, y=Y, z=Z, r=R, name=playername] is for an older version of minecraft - in 1.13/1.14 you use the /execute command.
For this you would use the command /execute if entity <Selector>[x=<X>, y=<Y>, z=<Z>, distance=..<Distance>, name=<Name>] run <Command>.
This will run <Command> if a <Selector> called <Name> stands in the position <X>, <Y>, <Z> up to <Distance> blocks away.