Scammed: How do you remove “go to assist” from imac

[Shampaincharly]

“BT “phoned from Delhi and got lucky because husband had reported a fault with broadband this morning. He had already had an automated call response earlier.
He put “go to assist “ on desktop on iMac and then they were taking him through some steps when he realised it was not right. He has phoned BT , confirmed it was not them.( Scamming CFS instead)
How do you get it off?

Is it showing in applications? Then just right-click and select move to trash.

Tried that.
Says can’t move open to trash.

Thanks talk fast

Husband has used force quit on it. Hopefully it will work.
Update: it has gone.