You can look at the following link of Teltonika Wiki to see an example of PPPoE configuration in a RUT device. Basically, you should go to option Network > Interfaces > Edit Interface > Protocol and choose PPPoE. This will give you the options to set up the PPPoE connection.
Setting up a PPPoE between RUTX and Mikrotik device - Teltonika Networks Wiki (teltonika-networks.com)
You should also make sure you are using the latest firmware (RUT9_R_00.07.01.4). You can download it on the following link:
RUT955 Firmware Downloads - Teltonika Networks Wiki (teltonika-networks.com)
I can't see interfaces option under network
I have already updated to a latest firmware as shown in image
Please, also change mode from "Basic" to "Advanced" on the top of the page so you can see all the options of configuration.