How to correct BME280 pressure data?

can anyone tell me, how the pressure data from BME280 is corrected (to sea level)?
Which formulae are used for this?
Currently I get a raw data of e.g. 978.6 milllibars which is displayed in the map with a value of 1028.1 ( altitude is 393m)
Thanks Dieter

We are using the following formula:
p0 = p(h) * (T(h)/(T(h)+0.0065*h))^(-5.255)
(Source: Barometrische Höhenformel – Wikipedia)

This should be included in one of our next firmware versions for the values shown on displays or the page ‘actual values’. To the servers we will send the raw values.

thank you, that’s it…