If the child ordinarily resides with you, you can apply for a recovery order through the court to have the child returned into your care.
Where there are no existing orders, a recovery order should be accompanied by an initiating application for parenting orders relating to the child's care arrangements.
If you remove the child from the other party's care without following the proper avenues, the other party will also be entitled to file for a recovery order against you.
It's important not to fight fire with fire in circumstances where the child has been removed from your care without your consent. Instead, it's recommended that parties follow the proper avenues for dispute resolution, rather than engage a game of tug o' war with the child's other parent. The court looks highly on parents who conduct themselves in such a way that they ensure the child isn't exposed to conflict or placed in the middle of the dispute, and it frowns upon unilateral decision-making by either parent.
For more information about recovery orders, see here:
Recovery orders