Rotating a squared matrix

[Clay Dragon]

Hi, I'm working on a image (Tile) editor in Qbasic and my Rotate 90 degrees function doesn't work for smaller selections within a bigger image.

So, to solve my problem I need to know how I can achieve this in QBasic:

We have this matrix and the selection I made and I wish to rotate it 90 degrees clockwise:

Before the rotation:


After the rotation:


Please help me!

Regards,
Clay Dragon