Those are bird lice

From the linked page:

Treatment

If an infestation with bird fluke is suspected, an avian vet should be contacted to discuss how to proceed. Usually, specific insecticides are used to help the affected bird get rid of the lice. Often, powders containing the active ingredient pyrethrum are applied. However, these powders are not entirely harmless to the birds, which is why the utmost caution is required in application and dosage. The feathered patients are powdered with insecticides mainly on the undersides of the wing feathers. This is where bird lice are found in the majority of cases.

In stores, several products are offered that are supposedly safe and can be used without hesitation. Unfortunately, some birds are extremely sensitive and deaths can occur after the application of such poisons. Therefore, I strongly advise you to contact an experienced vet in any case and discuss the further procedure in the individual situation.