There is no way extracting the first letter of the forename using mail merge
fields.  The best way to do that would be to put the data source into Excel
and then you can use the Left() function to populate a column with the first
letter.  While you are doing that there, you could also combine it with the
Title if there is one using the If() function in Excel.

That part of it can however be done using a field construction in Word as
follows:

{ IF { MERGEFIELD Title } <> "" "{ MERGEFIELD Title } { MERGEFIELD
Initial }" "{ MERGEFIELD Initial }" }

You must use Ctrl+F9 to insert the field delimiters { } and you use Alt+F9
to toggle off their display.

You are going to need a fourth field - Initial - which can easily be derived
from the forename field in (say) Excel - but not with Word fields.
The syntax would then be
{IF {Mergefield Title} <> "" "{Mergefield Title} {Mergefield Initial}"
"{Mergefield Forename}"}

Hi Alex,

You'll need to modify your data source to hold the initials as well as the
names. Then your mailmerge could use an IF test against the title to
determine whether to use the name or initials

Cheers