Mapping alt key

Dear community, 

I have a question about key mapping. I'm here struggling with my lefthanded co-worker to figure out how to find the right alt key to remap it. 

(windows pc)
Normally the left alt key when pressed while using brush let's you quickly use the eyedropper. 

She is lefthanded and would like to swap her alt key functions. 
So that the right alt key has this quick eyedropper when using brush. And the left alt key has the alt gr. 

We cannot find these alt key functions anywhere, so we don't know how to change them. 

Any suggestions? 

Thank you!