ESA 3 Form where to send?

I am on cont based ESA work group and received letter saying my 12 months would end june.
I called benefit office on letter and they said will in ESA 3 and when cont based ESA ends in June they will automatically swap me over to income based ESA as i will be entitled to.

Now where do i send the ESA 3 form as no letter or envelope was sent with form - my local office that sent the letter stating my benefit will stop in June?

Also if i fill in ESA 3 will they swap me over straight away or in June if i fill in form now?

Thanks in advance.