how to clear scale but leave size unchanged?

I have a mesh with X,Y scale set to 1 but Z is set to 3 - it causes that unwrapped textute is deformed. I found out that this is caused by Z scale - UV in Z dimention are just 3 times

Is it possible to set scale to 1 but without changing Z size? Just to clear scale data?

Not valid anymore - in Similar Threads I found Ctrl+a helps!