At the top of the bot under your details (name, pokemon, stardust, etc...) you will see the buttons (left to right) for Start Bot, My Pokémon then Set Coordinates...
Click the Set Coordinates and then enter the location latitude and longitude then click ok.
Ensure you are using the newest version of the bot, if not you can edit the Settings.json file using notepad++ or whatever you choose in the Cache folder of your PokeFarmer.