using two field in a same custom function

hi experts,

i have a query

suppose i have a data of 3 field

Name State city

tom gujrat varoda

billy rajasthan jaipur

jeny maharastra mumbai

jeny maharastra pune

now i want to change the city to "navi mumbai" where ever i find state = 'maharastra' i.e.

Name State city

tom gujrat varoda

billy rajasthan jaipur

jeny maharastra navi mumbai

jeny maharastra navi mumbai

thnks