You would first need to get a copy of the order but usually they are in force until the child gains their majority, usually 18.
I would seek legal advice from a solicitor as you will need to go back to court to get it revoked. in England this will be the Family Court , with a report from Cafcass or the local authority Social Work Department. In Scotland this is the Sheriif Court with a report from the Local Authority Social Work department.
The first step is to get your solicitor to contact the court to state your intention of seeking your child back.
Beware it can be a long and emotionally charged process.
Good luck