Leaking Roof, next steps?

[Chait Borade]

I had my roof replaced in 2020. We just had a heavy rainfall over the past week and my tenant notified me that their is water leaking through the ceiling into their laundry room. I checked the attic and and there is water damage from a 2 year old roof! There is no external damage i.e. tree falling down etc...

Who do I get involved to get the roof repaired? The original contractor who installed the roof? Or someone else to address the issue asap? I was also told at the time of installation that the shingles have a life time warranty, not sure how that comes into play here. Additionally, can I hold the roof installer responsible for the water damage? Has anyone ran into the same issue? Appreciate any insight.  

Thanks - Chait