Just go for it.
I went from car licence to Class 1.
Very first job after passing was collecting a trailer from a farm up a very narrow lane then take it to Romania.
I couldn’t get the trailer to move so I rang my (former) instructor & he rightly questioned whether I had taken the trailer brake off - I hadn’t.
No idea but no fear.
Map book routing, multiple currencies in cash, proper borders, payphones only (not that I bothered calling much), reversing onto ferry - all overcome as required.
My example may be extreme, but truck driving is never going to be the job you can have all the answers or experience for when you set off.