All router must have this feature - to either get DNS servers dynmically from your ISP, or to set static DNS IP addresses. I searched on Google but could only find limited information on the router model you have, but this is generally found in the Setup Wizard or Quick Settings of most routers.
We generally prefer clients to always use the DNS we push to their routers dynamically. This allows us more control to, if we do experience a DNS problem, refresh your session with alternative DNS while we resolve the problem.
Changing the DNS on your local PC may also work for testing purposes, but it is always best to set DNS on the router. If you are not able to achieve any change on the model you have, it may be best to borrow a router from a friend that does allow you to manually set these options.
Huawei might offer some support in South Africa, so maybe get in touch with their local distributor.