How to read temperature form the TMP36 sensor in C#?

As already mentioned, the TPM36 sensor provides an analogue output which is not supported by the Raspberry Pi.

So you would need an ADC (Analogue to Digital Converter) with an interface that is supported by the Pi. For such low speed data the commonly used interfaces which are provided by the Pi are I2C and SPI.

The board mentioned in the above solution uses the SPI interface. Such a board (or using the plain interface chip instead) is the best solution if you want to connect multiple analogue signals because these ADC chips provide multiple channels (8 with the above mentioned one).

If you only need to read a single temperture it might be easier to choose a temperature sensor that already has an I2C or SPI interface.

We can't tell you.
We don't have a "TMP36 Temperature sensor" and we have no idea how it is connected to your board - so we can't even begin to tell you how to read values. We can guess that it's connected via USB so will appear to C# as a serial port - in which case you need to look at the SerialPort class[^] - but other than that we can have no idea.

You should talk to the people who created it - they should provide technical support and will know more about their product than we will. If they don't, then find another supplier and demand your money back!