My zoom lens barrel was stuck and wouldn’t zoom out–it would stick at 100mm and wouldn’t move further in.
Start by removing the 4 screws at the back of the lens on the EF mount.
Then remove the 3 tiny screws inside of the EF mount, 2 hold the electric contacts inplace.
Now lift the EF mount plate up, you may have to rock it side to side gently, you won’t be able to lift it very far due to a ribbon cable so be careful.