How do you reset flashing airbag light after a tire change on my 2005 Toyota sienna?

I believe that you are talking about the "Flat Tire" light. It looks like the cross section of a tire with a double ended arrow inside it. If so there is a procedure in your owners manual to follow after you change tires. The flat tire detector actually used the antilock brake sensors to note when one tire is rotating at a different speed than the others. If you have one new tire it will be bigger around than the others and rotate slower. The procedure in the manual will tell the computer that everything is normal. So check and correct your tire pressures beforehand.