The F1 error code on most Frigidaire gas ranges indicate either a failed electronic oven control board or a problem with the oven temperature sensor probe. Without a model number for your range, I cannot be sure.
unplug the range
and check the oven temperature sensor probe. On most of these types of ranges, you can access the wiring disconnect for the probe by removing the screws that mount it to the inside back wall of the oven. Carefully pull the probe into the oven until you reach the wire harness disconnect plug. Unplug the probe but do not allow the wire harness to shrink back through the back of the oven. Use a volt/ohm meter to check the resistance of the probe. You should measure about 1100 ohms of resistance through the probe at room temperature. If not, then the probe is likely causing your F1 and it will need to be replaced. You can order parts from the
website. Use the full model number of your Frigidaire range to order the correct part.
If the probe is okay, you could have a wiring failure between the probe and the electronic oven control board or you could have a failed control board.
If you need more help, resubmit your question with additional details and the full model number of your Frigidaire range.