Tip:
Create a piano accompaniment from a leadsheet that has only a melody and chord symbols.

The issue:
You have a leadsheet. Your keyboard player does not read from only melody and chord symbols. You need a keyboard chart.

Solution:
Using one of the Plug-ins, Sibelius will create an appropriate keyboard part for you.

Here's the leadsheet: a melody line with chord symbols.

Remember, the Plug-ins in Sibelius are NOT undo-able, so Save the file BEFORE applying the plug-in, so you can revert back to it if this plug-in gives you unexpected results.

Select the entire piece (triple-click on the staff).

Go to Plug-ins> Composing Tools> Realize Chord Symbols and Diagrams

Set your options for the type of part you want to create: Piano or Guitar; How many voices, and style of chords.

These are the styles that can be created when selecting from the "Chord Style" picklist.

Here is our piano part, the result of selecting "8th note Alberti" from the Chord Style picklist.