How to change the default_tx_power of SDK15.3 ble_app_att_mtu_throughput test?

[ndc_bee]

I am doing the throughput vs RSSI test, but I don't know how to change the default_tx_power of the board act as tester?

[awneil]

https://devzone.nordicsemi.com/f/nordic-q-a/37928/just-set-tx-power