Lumi Max OCR sequence to convert scribble underlines to neat straight lines

Hello;

I own a Onyx Boox Lumi Max and I was annotating (scribbling) an eBook, underlining by hand sentences which I deem important

I do not know the sequence but I accidentally activated a feature whereby Onyx then converted my shakly handwritten underlinings into neat straight lines.

I've tried many actions and am unable to duplicate or activate the feature again

Does anybody know the sequence and how to activate the above feature?

Warmest Regards
Steven Sim