The best way , prob, is to focus on that true south satellite for you, which would be 89 or 87, and try to locate it. You might have to alter your elevation and/or your dish angle by a few degrees, to hit the satellite. Those angle-indicators can be pretty close, or some can be off by sev degrees. Start with motor on zero position, USALS to move motor to your south satellite, then start looking for signal. You might have to pan the dish/motor assembly east or west a little bit from where it stops, if you get nothing, adjust your dish elevation up or down one degree, pan back and forth again. It takes patience, and with a little exploring you will hit that first satellite. After that, it does get easier!
edit to add : Yes 91 is a circular satellite, but there is a linear satellite at 91, Galaxy17, it has a few ku channels. And yes, the dish will be looking as if its pointed straight ahead the further west it goes (in our part of the country, at least). Offset-dishes look at the satellite arc, but at about 22degrees lower "look angle" than a big c-band dish.