Ac vent blowing less air

I have a 2003 celica gt

Its blowing less air from vents everythng is fine even blower motor it
I believe theres some leakage in the air duct

I found some soft pieces of plastic in the passenger side were should i start inspecting

It was on the ground and slowly slowly i found lots of chunk on oassenger side floor mat i believe its the chunk can some1 send me a link on how to do it withoutbripping the whole dashboard