Tongue pulls back slightly from the T position, blending into R. Sounds close to 'chr'.

Americans pronounce trainer as TRAY-ner (/ˈtreɪnər/). In "trainer", the "tr" cluster blends into a "chr" sound — a natural American English pronunciation. This is called the TR Sounds Like CHR, a hallmark of natural-sounding American speech. It comes out as TRAY·ner. Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "He hired a personal trainer to help him lose weight and build muscle".
Record yourself saying "trainer" and play it back. The mic stays on your device — nothing's uploaded.
2 syllables, 5 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
Tongue pulls back slightly from the T position, blending into R. Sounds close to 'chr'.

Curl or bunch your tongue without letting the tip touch the roof of your mouth. Brace the sides of your tongue against your upper back teeth, and round your lips slightly.
Start with your jaw slightly open and the front of your tongue forward and slightly up. Glide upward, your jaw closes a little more and your tongue arches higher toward the roof of the mouth.
The textbook way isn't wrong — it's just not how anyone actually says it.
In "trainer", the "tr" cluster blends into a "chr" sound — a natural American English pronunciation. /t/ shifts toward /tʃ/ ("ch"), so TR sounds like "chr".
Stress falls on the first syllable, not the others. Stretch TRAY — keep everything else short and quick.
Americans use a relaxed retroflex R — the tongue curls back rather than rolling. The R is one continuous sound with the vowel before it, not two separate sounds.