According to the GATT Specification Supplement, Chap. 3.222 Temperature Measurement, the data type is medfloat32, which is defined in IEEE 11073-20601.

Here is a description of how to convert a float value: https://stackoverflow.com/a/60843099/8124605

For example, a value of 25.63℃ can be coded as

Exponent: 0xFE -> -2

Mantissa: 0x000A03 -> 2563

uint8_t ess_temperature[] = {0x00, 0xFE, 0x00, 0x0A, 0x03};