Good evening delwinsr
You haven't said what seperator there is, but for the example here I'll assume it's a space.
=RIGHT(D11,(LEN(D11)-FIND(" ",D11)))&" "&LEFT(D11,FIND(" ",D11))
The above is the formula you need but you might have to tweak it for your ranges etc. Put the formula in a spare cell and copy it down, and then if you need to, you could copy it back over the original range using copy - paste values.
HTH
DominicB