Pairing A7751 keyboard

I have been trying to pair this keyboard for weeks. The first time I did they flashed a pin but when I clicked next the PIN disappeared and when they asked me for it on the pairing screen I didn’t have it. I have tried holding the bluetooth key down for 10 seconds but every time I try to pair it asks for the PIN. I need to remove the original pairing request abd start over or the keyboard can never be used. ANy ideas?