There is no way to add an offset and it would not make sense because the altitude shown here is the result of different sensor values from IMU and baro. Usually with acceleromter calibration this will be corrected but still there is temperaure drift depending on temp compensation at barometer chip and possibly IMU heater.
With the new GUI that we have now, we can see the IMU temperature. It should increase slowly during initialization. But if the bias of the accelerometer is too high, nothing will help, heater or not and accelerometer calibrated or not. But I still believe that accelerometer calibration can prevent accelerometer problem when done before the bias went out of control.
Just for test I have here an IMU with only ~650mG on Z-axis of the accelerometer. In this case nothing will help. The AHRS subsystem flag (Attitude Heading Reference System) is not set and the FC raises following error message: "WARNING Diagnosis: AHRS Not Ready". Also the EKF status is zero. With other words the drone is unable to determine its attitude in the X-Y-Z orientation. and is not able to fly.
View attachment 31632
New GUI gves deeper insight now.