Remember: Please note that most T-Beam/SX1278/SX1268 (example) modules are not able to output more than 22dbm, you need an amplifier (it also improves RX). To improve radio RX, I also recommend a bandpass filter for 868 MHz. Remember that the amplifier does not have to be effective, ultimately the other party will hear you but you will not receive the signal from them, which is very likely, so consider upgrading your antennas.

1. recompile firmware
2. open firmware/src/mesh/RadioInterface.cpp
3. find line that contain text "DEF(EU_868"
4. change to RDEF(EU_868, 869.4f, 869.65f, 100, 0, 30, false, false, false),
5. in same file look for

       if ((power == 0) || ((power + REGULATORY_GAIN_LORA > myRegion->powerLimit) && !devicestate.owner.is_licensed))
           power = myRegion->powerLimit - REGULATORY_GAIN_LORA;

6. replace this code with

   power = loraConfig.tx_power;

I assume you know what you are doing and keep your radio space clean. In case of high radio noise, try to reduce the operating parameters.

how to compile using visual studio code: https://meshtastic.org/docs/development/firmware/build/