Reset company code Data

System is showing this because you have posted documents to this company code.

Process to reset company code data is to use transaction OBR1 enter your company code and reset the data.

Secondly, use transaction OBR2 and delete all GL accounts.

Now you will be able to assign different chart of accounts

but this will be hazardous since you will not be able to change Chart of accounts in Controlling area. So you will have to delete your chart of account through a lengthy process. Or you create the new controlling area itself.

If there is no controlling area then you can go ahead.