1) Wait for the club to make an offer, then you can change the transfer fee for the player. however if u change it to a ridiculas price then the chance of the other club signing ur player would be small
2) go to the players profile and click on the link on bottom left coner 'Offer to Clubs' then you can also change the transfer fee like the top. wait a few days then the interested club will match ur offer (or they maybe not make an offer as the price is too high)
PS: selling ur player by the interested club offering u will give u more money than u offering the club(s)