tare of siwarex cs

I have a problem with the tare of siwarex cs .
min. weight = 20 , max weight = 1400 . After calibartion ( zero and weight 1 of 500 KG ) it is okay .
But after I remove the structure made to hang the calibration loads , I got about -100 kg. This is the weight of this structure . I am not able to tare this value unless I increase the max weight above 10000 kg . and change to "----" instead of OIML and make the -ve % = 10% instead of 1 % .
However even after that when there is power off and on , the -100 kg returns back and each time we have to tare it again which is not accepted . Please advise how can I tare this negative value or make it zero permanently after calibration .