Click the ticker symbol in the sidebar, then click in the toolbar.
Swipe left, then click in the toolbar, then deselect the tickbox next to each watchlist you want to remove the symbol from.
Go to the Stocks app on your Mac.
Move the pointer over a ticker symbol in a watchlist, swipe left, then do any of the following:
Add the ticker symbol to watchlists: Click Change the chart display in Stocks on Mac