Okay we still don't know the make

hmy:
Remove the inner tube. You will have to disconnect the pipe work first. Make sure you note carefully how each joint is assembled including the o rings. They are tapered. Once removed see up the ports and gently partially inflate and locate the leak . A bucket of water will help.
Repair kits are available but maker specific. Quite frankly a new tube is your best bet.
Hope this helps. It really will help if you can tell us the make.