@certificate, @exp_date = certificate_with_date(@int, @coach)

undefined method `certificate_with_date' for #<#<Class:0x0000564473b34af8>:0x0000564473b31ec0>

helper_method :certificate_with_date

def certificate_with_date(num, coach)
    if num == 1
      return 'DBS', coach.DBS
    elsif num == 2
      return 'Safety', coach.safe_qual
    elsif num == 3
      return 'Coach', coach.coach_qual
    elsif num = 4
      return 'First Aid', coach.first_aid
    end
  end