I just clicked on Private Messages under Welcome, Davydd or Welcome, Peteco for you and got a screen with a "Your Cotrol Panel: Private Messages: Send New Message" that brings up an input to type my message and a Recipient Username to send it.
There is a little checkmark list of things you can check such as a recipient notification or saving your message that needs to be checked.
Your Control Panel brings up many other things you can do in this forum.
2021 Advanced RV 144 custom Sprinter
2015 Advanced RV Extended body Sprinter
2011 Great West Van Legend Sprinter
2005 Pleasure-way Plateau TS Sprinter