Again, similar situation to what you posted here:
viewtopic.php?p=130355#p130355
Think / plan further ahead
There's signs indicating an exit at 1600, 800 and 400 meter in Flanders, and 1500; 1000, 500 m in Wallonia
That should give you time to go to the right at an appropriate time
If it's busy and other drivers have already moved into the right lane to take the exit, you weren't looking / thinking / planning ahead enough
If you want to keep overtaking while you need to take the exit, make sure there's enough gaps in the right lane to safely slide into.
And keep in mind that others (like me

) may be doing the same thing and closing those gaps
Don't slow down so much that you force drivers into overtaking you on the right
Slowing down much will also have a ripple effect on your own lane, way behind you
(the infamous accordion effect that may cause drivers behind you to have to stop, even if you never did)
If it doesn't work out, continue ahead and take the next exit to turn around or use another route.
Be careful when taking a late exit between trucks
https://www.youtube.com/watch?v=6-0E2Nxtm6o