The conversion

135°F = 57.22°C

°C = (°F − 32) × 5/9, so (135 − 32) × 5/9 = 57.22.

As an outdoor air temperature, 135 °F sits in the hot band. The other scale is on the dial beside it in the app, so a reading like this needs no conversion at all.

Convert something else

68°F

The range either side

Neighbouring values, for when the number you actually wanted was a degree or two away.

Fahrenheit to Celsius either side of 135 °F.
FahrenheitCelsius
130 °F54.44 °C
131 °F55 °C
132 °F55.56 °C
133 °F56.11 °C
134 °F56.67 °C
135 °F57.22 °C
136 °F57.78 °C
137 °F58.33 °C
138 °F58.89 °C
139 °F59.44 °C
140 °F60 °C

The other direction

57.22 °C converts back to 135 °F, which is the same relationship read the other way. Going from Celsius to Fahrenheit, multiply by 9/5 first and then add 32. Adding first is the usual mistake.

The full converter handles any value, in either direction, including kelvin, and shows the formula as it works.