HOW TO PUT WIFI SPEED LIMIT IN D-LINK ROUTER?
Follow the steps to put wifi speed limit in D-Link routers:

Go to advanced > Traffic control

You will see a section there that will be named QoS Rules click on the Add button

Now paste the IP address which you have copied from the wifi users list and want to put a speed limit on it.

Paste the IP address to the Source Ip and change the Up floor, down floor, Up ceiling, and Down ceiling(the name can be changed depends on the company) to whatever you want.

For example, you want to limit the users to use only 1Mbps speed then write down 1000Kbps and click save/add.