How to add icon tray

[LeGIoN_LiLa]

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[R_S_4]

Would be nice to know which software you use and which tray you mean.
The easiest way is this:

Start...Settings...Today...Items

Here you can scroll and pick the items you want.
Hope this helped!

[Rudegar]

if he mean the button bar of the pda
then there is no default way
some programs add icons there

maybe you can search for an application which let the user
add icons there themselfs