i averaged 62% in my second year which is worth 33% and want to graduate with a first. What average do I need in 3rd year to get a first.
Based solely on the information you've provided (which is almost certainly insufficient*), you would need 74% in your final year, as (0.33 x 62%) + (0.67 x 74%) = 70.04%.
* Many universities have complex rules around degree classifications. They'll sometimes only look at the best N credits across both years, or will ignore the worse M credits in a given year, or will round things or weight things in odd ways. Without knowing your university, we can't tell which of these rules (if any) apply.