I was changing the chain and stupidly had not released the clutch brake.

Any ideas as to how I release the band enough to get it back on, guessing I am not the first one to be so stupid.

Don’t worry, a lot of people do this.  Here’s how to fix it:

Put the cover back on as far as it will go.  You don’t have to force it.  Now, hold the chain brake handle out, in the position it would be in if it were tripped.  Now push together the part where the dogs of the brake handle engage the dogs on the cover.  You may have to squeeze them together hard.  The goal is to mesh the dogs together and pull back on the brake handle to unlock the brake.  Channel locks may help.  I’ve had pretty good luck doing this.

Many thanks, worked a treat.

Now all I need is somebody with a stump grinder.