Also in Japan, There are many convenience stores. Moreover the number of stores and service levels are far better in Japan than in the Philippines.
The convenience store is usually called “Konbini（コンビニ）” in Japan.
Well, When you try to buy a boxed lunch or a prepared dish you will be asked in Japanese as ” Atatamemasuka?” This means “Do you want this warmed up in a microwave?” Therefore please answer by “hai（はい=Yes）” or “iie（いいえ=No）.”
Also, you are not asked by a clerk, but when you want to warm it up say “Atatamete kudasai（温めてください）”.