You have to wait for an email from IG... It will set out how to accept. Also as a custodian, they only do in batches so you may be waiting a while to be allocated the WAM shares in your account from when you accept. This is also one of the reasons I don't use IG for any corporate actions.
I bought some AYS in my IG share trading account. Can I accept the WAM offer?, page-5
Add to My Watchlist
What is My Watchlist?