Vauxhall Corsa auto flashing n

Sounds like a faulty selector switch to me, best bet is buy a haynes manual and remove the switch and clean it/regrease and replace as per instructions.
If you are not confident about doing it ( its not hard) then see if a mate can do it for you.

Get it scanned and see what fault shows , otherwise just guessing .

Whittinghame`s suggestion is a good idea, although be wary of dtc`s if any, that show allkinds of strange faults as the selector is mechanical in operation and should not show on a scanner, but may throw up other problems which will be cured once the selector is sorted.
A decent mechanic should be able to differentiate this.

I know this sounds daft but its true,my son has the same car the auto light started flashing on his dash so he stopped,the car went into limp mode,(puls off very slow hardly moving,so he phoned me,could not fix the problem,phoned the AA ,he changed the back light and brake light,car fixed he said the back lights are conected to auto box ??? sounds daft but it worked,he now carrys spare bulbs for the back lights(brakes),he went straight to the back of the car as he got out of his van and took the light cover off