So I went to start my car this morning And found once it came off cold start it struggled to run. I know the car has always run a bit lean so I'm thinking that it was just not rich enough to run in the cold air. So is there a way to richen up the mixture.

anti tamper bung on the air flow meter is covering a screw you can turn to alter it , or more advanced mess with the spring tension inside the air flow meter , best to only fiddle with it on a gas tester machine

some reading here....https://www.thesamba.com/vw/forum/viewtopic.php?t=356377#:~:text=The AFM has 3 things,screw on the throttle valve.