P0455 code large leak detected?

I have a p0455 code large leak detected. I also get message on the dash to tighten my gas cap which I have gotten since buying the car 2 years ago. I have already changed my maf sensor. Where is the evap emissions purge valve located. I am recently widowed and disabled. If its easily accessible i may be able to change it out myself. I have inspected what hoses i could see. I cant access the airfilter does that black cover need to come off ? Until i can get it repaired can i still drive the car . I need to work.