Yep, that's verdigris! Use a toothpick soaked in VC and apply a drop on it so a dome forms. Let it sit for about 10 minutes (do not let the VC evaporate) and work the spot with the toothpick to see if it is removed. Dab off the excess and inspect it. Repeat if necessary. Take a pic of the results so I can see.

It looks like it's pretty thick. It might require and extended soak. I'll pass judgement after see the results of the spot treatment.
Lincoln Cent Lover!VERDI-CARE™ INVENTOR
https://verdi.care/