To read the fiber attenuation on your mikrotik router, you either have to go to your mikrotik gui (Winbox) app and open a “New Terminal” or connect through telnet to it and type this:
/interface ethernet monitor sfp1
If you see the things below, they should be low. below -10 tbm… maybe -7 on receiving rx and 5 tx.
If you don’t see them, you might have to scroll down with the down key on your keyboard until you see this: