Assuming you have filled in the application through
www.atcocareers.co.uk then thats what you need to do. Visiting a unit is not just a case of turning up - there is security to consider, as well as people available to host etc etc. Best way is to get the contact number for the tower from the UK AIP.
However, I would suggest at least getting a reply and a stage 1 course datebefore visiting a unit. plenty of people fall at this hurdle and its a long way to the finish line.
Also, There is no way you will get a course this year. In fact, im not convinced you'll get a course next year. A job as an ATCO with NATS is as close as you can get to a job for life, with excellent pay and pension provision, good working conditions and a varied interesting role. With all of the above, as you can imagine with the current state of affairs over the past couple of years its fair to say interest has shot up somewhat.
Thats not to say you shouldnt apply, but you need to be realistic. Applications have only just opened and some poor souls have already been on hold for 18 months.