Usually the bluetooth device will have a pin code.
Step 1:
Please, check for pin on the following:
i. On the accessory package,
ii. In the accessory manual or instruction book,
iii. On the front/back of the accessory itself,
(I found mine on accessory manual)
Step 2:
i. First enter pin in main device (pc/laptop/mobile/etc) and press Enter. It will show "device is connecting" or similar,
ii. While it is showing "connecting", at the same time just enter/type-in the same pin in the bluetooth keyboard/accessory and press enter on the keyboard/accessory.
iii. Both devices will now be paired/connected.
(If no pin is found with the accessory, you can try default pins such as 0000 or 1111 or 1234 etc. Or look in-to manufacturers website for FAQs)