Other than needing the normal documentation for your own recovery truck, as listed in the first few posts, I’ve no idea what you’d need for a recovery job.
You will need a Eurovignette for the part of your journey across Belgium and/or Holland to get to Germany.
This is a daily tax of £5 or €8 per day. You can buy it on-line now at Eurovignette
You’ll also have the road toll for Germany to pay to get to Poland.
You must have prepaid this before you join the autobahn system, there’s a hefty fine if you’re caught without it. Plenty of gantries to catch you even if you don’t see anyone.
It’s called MAUT, the toll is calculated on the Euro class, number of axles and the distance covered.
You can get some info here HGV-Toll-Germany
You pre-book your route, the machine looks up the shortest route from your entry point to exit point. If you don’t like the route it gives you, add in via points to get the route you want now.
Once your route is booked, you have to stick to that route. Again, being caught off route is liable to a hefty fine.