Question, have you made sure that they are compatible? Not all keyboards work with all tablets (although it is assumed they would). If you did make sure of this, then to pair them try the following.
Wireless Bluetooth
Linking or pairing a wireless keyboard can be easy, or difficult, depending on a few different factors.Factors like the operating system of the tablet and the brand of the keyboard.
For tablets that have built-in Bluetooth capability you should be able to use the steps below to pair them. This is general pairing information. It may vary slightly for different brands or different tablet OSs (Windows, Android, iOS, etc.).
To pair the keyboard to the tablet.
1. First, make sure the wireless keyboard has new batteries. Old or drained batteries cause this to not work correctly.
2. On Android tablets, go into "Bluetooth settings" and click "Find Nearby Devices." (This isn't necessary for iPads.)
3. Now turn on the wireless keyboard. The LED light should turn on. (Depending on the brand & model, it may turn off after a few seconds. This is OK.)
Apple keyboards do not have any other button (and the light should begin to flash immediately), but other brands and models may have a "Connect" button.
4. If yoru keyboard does have a "Connect" button (if you don't see it, check the back of the keyboard, sometimes it is located there). Press the "Connect" button. T
This should make the Bluetooth LED light flash. A flashing light generally means that the keyboard is "discoverable." Some brands and models don't have a flashing light. It isn't necessary.
5. Once the light is flashing or is completely on (in the case of one without a light, give it a good 20 seconds after turning on), wait for the device to appear in a list of Bluetooth devices recognized by your tablet.
6. When you see the keyboard listed, select it. A pin number, for you to enter into the keyboard, will usually appear now on the tablet. This is to make sure that the device you are paring to the tablet is actually authorized by the tablet user.
7. Enter the pin number, shown on the tablet, into the keyboard.
The keyboard should now be paired with the tablet.
This means they should "recognize" each other every time they are powered on within around 30 or so feet of each other.