First advice: Drop Blitz3D, its decades old.
Second advice:
To draw the FPS you first need to calculate it, add this code into your main loop.
if (millisecs() - fpsTimer > 1000)
fpsTimer = millisecs()
fps = fpsTicks
fpsTicks = 0
else
fpsTicks = fpsTicks + 1
endif
And delcare the 3 variables needed to run this (fpsTimer, fps, fpsTicks) in the global loop or some where out of the way. Then to draw it just add this in your rendering function.
Text 5,5,"fps: "+fps
(Please note, I haven't used B3D in a while, so there may be a few syntax errors in the above code)