In the transfer menu, click on the "Negotiation" tab and there you go.

Before making an offer, check the manager level of the team. For a quick and successful transfer, that manager should be at least 1 level higher than you. The greater the level difference the better chance to succeed.

Also, for younger players most people don't take 0 token offers, so you should try to make an offer of at least 1 token, that will cost somewhere around 9 tokens for you depend on the player's market value.

If you don't want to spend so many tokens, you may make 0 token offer to older players if their team are many levels above you.