Let's first remove the carriage, which is the top part with all the number wheels on them.

Position the calculator so that its keyboard faces you. This orientation defines the left and right sides of the calculator.

Unscrew the lower left screw on the left side of the carriage.

If it just keeps turning, you may need to insert a screwdriver on the other end of the shaft that this screw is connected to, the one on the lower right of the right side of the carriage. Don't turn it! Just turn the left side.