Train 5 star player

I have a Russian 5 star striker aged 25 called evgeny chernov and he has a 1 on 1 special ability but could I train him to a six star and can you do this with any 5 star players

I wouldn't bother starting any power training with a 25 year old tbh... Unless he is a very important player for you.

I'm new to this game and play on iphone and what is power training. But I do know the basics I won the first season and I'm in my 2nd season, so what is power training and I'm on iphone not computer

Power training means using the green packs to replenish your man instead of letting him gain condition normally.
You use 6 x stretching, 2 x cardio and 1 practice match every hour, on 'hard' intensity.
Repeat until the man is at the level you want.

Ideally you only want to do the extra training on a fast training younger player that you intend to keep for several Seasons.

A 25 year old can accumulate a good number of skill points over the season and probably can maintain a 5 star for a few seasons. (If he is a good ST)

If you play him everyday in every match, he may get to 6 star, no problem, but I would be happy if he maintains 5 star for 2-3 season.