Can we set price different for the first year and onward? Like, for first year 2.99 and then 0.99

Find that app/IAP in App Store Connect, then choose 'Pricing and Availability', then select 'Plan a Price Change' - looks like max now is Dec. 31, 2020.

If you are asking ‘can we change the price of an IAP for everyone at a specific date the answer is yes. If you are asking can we change the price of an autorenewal subscription IAP for each user after each user’s introductory period the answer is also yes.