What to do in Ruby on Rails if the class (instance) method is not visible inside the class?

Question

Ruby on Rails

For example, I use the Parallel technology, inside a method of a certain class:

Parallel.each(list, in_proceess: 3) do |item|
my_method(item)
end

Here my_method is another method of the same class (instance), and it is not visible in this technology.
What can be done in this case?
Making this method a class method and using it is not an option.