If your present router is a Tenda router, then in that case you can take a look at the Tenda documentation on how you can Tenda ac1200 setup as an access point. Or else, you can make use of instructions of a particular manufacturer for another router brand.
Step 1: Link the access point of the Tenda router to the current router by using the ethernet wire. Connect it to the yellow-colored LAN port of your router.
Step 2: When you are linked to the router, launch your internet browser. And type the IP address. This will open up the access point setup page.
Step 3: Click on wireless settings. This will show up the modes that one can use. After that, choose AP repeater.
Step 4: After that to set up a Tenda access point as a repeater, change the name of your network or you can let the default setting remain. In case, you are using a repeater, then the best thing to do is to change it. So, in that case, both the devices are not going to have the same name.
Step 5: Go to open scan and click on it. When completed, it will show up all the routers that are there in your area. Choose your router and then click on apply. The access point will start rebooting when it gets connected. This will help you to setup Tenda ac1200 repeater mode.
Step 6: Remove the ethernet wire from the router and take the access point to a position where you can use it as a repeater. The access point needs to be within the range of your present Tenda router, so that it starts repeating the signal from that position. So this is how you can setup Tenda access point as a repeater.