That will depend on what the stains are...its hard to tell from pic.
There are a few tests to perform. If you ave a puck, test tat in a sock on a stain for a few minutes. If it lightens, its organic stains and may lighten with FC and sun over time.
If its iron (doesn't look like it to me), some crushed up vitamin c in a sock should lighten a test area.
If its copper (blacker areas could be) then a dry acid test in a sock would lighten it.
Alternately, you could purchase Jacks Stain Test kit to determine the best stain removal approach.
My pool isn't plaster so I'm not deeply experienced with this, but I will link you to a tool I've witness, via thread, others have used to successfully do an "underwater acid wash" on a plaster pool.
Don't rush in deciding the plan...you've got to make sure that messing around with the stains doesn't end you back up in slam territory, because if the stains are metal, having to slam again can undo the recess.
So here's the tool to look at and read reviews:
https://www.amazon.com/Purity-Pool-UAW-Underwater-Acid/dp/B00C7UGLFY
And here's another TFP stain treatment if metals (but works best on iron, not copper) to read up on. I would wait at least a week or so because th AA will eat your chlorine and after years closed we want to be certain nothing can start growing again.
Ascorbic Treatment to rid Pool of metal stains
While you study up on stains, test them, etc., keep your water balanced and your FC to the TFP ratio...take a cruise through pool school again as a refresher.
Post us a compete set of test numbers I the next while, eg TA, CH, CYA etc.