Don't look at his postition according to Rocking Soccer, look at his skills/potential instead.
Take the player you received today, for example.
https://rockingsoccer.com/en/soccer/info/player-2133208
According to Rocking Soccer, he is a forward. However, you can just as well make him a goal keeper if you want. He'll become a goal keeper within a few matches. So don't look at what RS says, look at the player instead. This player can be a good forward or goal keeper because his speed is higher than his power. However, because he's hot-tempered, it could be a risk to make him a goal keeper. You'd probably want to train him to be Correct.
So these should be you considerations. In what position do you need the player most? What are his specials? What are his fixed skills? Etc.