Using the I2C connector on the BTT GTR 1.0 board

[DEAth1981]

When I try to use the i2c bus (pins PH7 and PH8) on the BTT GTR 1.0 board, I get an error message from Klipper that says " Unknown i2c_bus ‘i2c3’ ".
According to the board pinout scheme, PH7=I2C3_SCL, and PH8=I2C3_SDA.

The problem is that when compiling the firmware for BTT GTR 1.0 (STM32F407) in the part of the i2c implementation, the code from STM32F1xx is used (and this chip does not have i2c3), then in the compiled firmware the i2c3 implementation is completely absent for BTT GTR 1.0 (STM32F407).

How to use the I2C connector on the board?