Drain it! or atleast suck out the required amount (if its only a little over the full mark may be OK but why take the risk).
I did this once, many many years ago with my first TR7 (when I was young and ignorant

), I had a severe oil leak and topped it up too much. Ended up with severe piston slap which took months to sort out even when the oil level had been corrected. Probably could have been much worse.