Make a trap like a big basket or box with one end propped up with a stick with a string attacked you can pull from far away to drop the basket down onto it.
Put food in a bowl under there and wait till it goes it.
If you then keep it in a cage and really feed it up so it gets fat and strong, it probably will want to fly away back to its mate and coop once healthy again, as its very hard to train an adult homing pigeon to a new place anyway.
At the moment it looks weak and tired out. It does not have the energy to fly off.
Good luck.