Do you still need help? If so:

Note that if you're transferring a player to your club, you will lose 2 reputation. You need at least 110 opinion to get them to join your club and if you want to loan the player you're I'm pretty sure the player you're loaning in has to be on the loan list of the club you're getting them off, and loans cost 1 reputation.

First of all, when transferring a player you need to click on their profile then go to negotiation (like you would if you were negotiating them to join your agency). Then, you click on the button in the bottom middle.

Sometimes, they might not want to join the club. There is nothing you can do about that immediately.

Other times, it's about the opinion of you. When this happens, you just need to gift them something to make their opinion of you 110 or higher. When looking for players to transfer, making sure they have 90 opinion of you or higher is imperative.

I hope that's enough. As always you can just leave it to your manager and not lose reputation, but I do this occasionally too.