This can be obtained by either emailing directly the ISA Team, isa@trading212.com
They will also provide you with detailed instructions on how which forms need filling out.
Remember to always use a ISA Transfer form when transferring previous years subscriptions.
If you are using your current years subscription (Ā£20,000) then a normal transfer will do.
Alternatively the account number can be seen by going into ādeposit fundsā section, select bank transfer. And the reference code will be your ISA Account number.
To be safe though, just send an email.
Any queries, add them to the email to Trading212.