It's difficult to understand the problem you have.
Either the termination of the aerial cable has come apart from the cable - OR - the aerial connector inside the TV set has fallen away from its mounting - OR - you have a telescopic aerial that's become detached.
If it's just the cable then a new termination is easily fitted with no soldering required - else buy a new ready made cable.
The other two possible problems are also relatively easy to solve but will require the set to be dismantled so that you can get inside to do the soldering.
All the pieces you need can be got from a hobby electronics store - or Amazon.
Good Luck..., June 2017
