Betta Fish: White spots on my betta fish

Hey guys, let me give some background real quick. I have had this betta fish for about like 2 months. He was given to me with fin rot and the store told me he had basically been in that small container for about a year or more (depressing, I know.). He is in a 10 gallon tank with a nerite snail and 3 shrimp who are doing very well. The parameters of the tank are good as I just checked them and all numbers are clear. The problem is I came back home this afternoon to notice these small white dots on the back of him. I have never really dealt with this issue for any of my bettas. Do any of you know what this could be or how I can treat it? I am very worried and open to anything. Thank you for any help.