The word "if" is always pronounced with the stress on the second syllable: "ɪf".
If you are hearing "if" with stress on the first syllable, it might be:
* A mistake: People sometimes mispronounce words, especially if they are not native speakers.
* A regional dialect: Certain dialects of English might pronounce the word differently.
* A specific context: There might be a specific reason for stressing the first syllable in a particular situation, such as emphasis or a dramatic effect in a poem or play.
However, in general usage, the word "if" is pronounced with the stress on the second syllable.