@Saytu 

If I understood you correctly you want to set up a bandwith limit  on your guest network even though you said you want to stop your neighbour using your wifi? 

If giving your neighbour your guest network details they still will be using your wifi. 

I would personally change your wifi name and password then restart your router and your neighbour won't be able to use your WiFi. 

Failing that if you still want to give your neighbour your guest wifi details but want to restrict the download and upload limits then 

Open up the tether app and click the menu bar at top left of screen, 

Open the guest network tab 

Create a guest network name amd password, 

Next to each of the network names there should be a little circle with a i in it click on that and then select the bandwidth control. 

Then enter the max limit that you want to impose 5,10,15,20mbps max limit, save the settings then you can test it by logging onto that wifi network do a speed test and it should if done correctly only max out to rhe speed you set it at. 

If all done log back onto your main network and if you choose to give your neighbour the guest wifi details them you'll know it is restricted to what ever speed limit. 

Make sure you have changed your main wifi network name amd password as your neighbour will be able to log back onto that network and use full speeds ect 

I'm not sure if your version of tether app has this aswell but on my version I can go onto the client page find a certain device say your neighbours select it and you should see a option that says speed limit. 

Select that then you can set a speed limit for that device