Welcome to the forum.
You can usually use Shell to do that. What is the DOS command
echo ^G > COM4
the character before the G is done in dos by holding down the crtl button while pressing G
You can probably use something like this:
Code:Shell "Cmd /k echo ^G > COM4", vbhide
I can't test, but does this work?
Code:Shell "Cmd /k echo " & chr(7) & " > COM4", vbhide
Cmd runs the command prompt.
The rest is the same as you would type at the command prompt, other than the ^G can't be typed as a literal ^ sign followed by a G, it's actually (according to my searches) equivalent to the ASCII character code 7, which is what the Chr(7) part recreates.