Erg mode missing from menu

Please help. Hey guys- I wonder if anyone can help a brother out?
I swift using my watt bike Atom. I have recently joined in some workout meet ups set up by a wonderful local athlete. I must admit I’m no wizzkid with gaming or computers. I seam to have lost the ERG mode button on my bottom menu. I can only use my gears to try and maintain intervals above ftp etc.
Please help …