Can I uncheck box7 checked it by mistake cannot continue how do I correct this?

There is not a box to check/uncheck for Box 7 on the Form 1099-R.  You enter the code in Box 7.

There is a IRA/SEP/SIMPLE box that be checked or unchecked.  Is that the one you mean?  If the program does not allow you to remove the check mark then delete the Form 1099-R and re-enter the form manually.