Assuming that when you left the Church, you had completed the initiatory sacraments (baptism, First Communion, confirmation), all that is needed to return is confession. Even if you did not commit a mortal sin by leaving, through lack of full knowledge or lack of full and free consent, sacramental confession will grant you supernatural grace and will strengthen you against future temptations to leave. You are free to go to confession to any priest you wish, whether it be one you know and like or one that is available through your local parish.
If you have not yet completed the initiatory sacraments, speak to the pastor of your local church about preparing to do so. For practical reasons, most parishes ask Catholics in this position to enroll in the Rite of Christian Initiation for Adults (RCIA); but, if your pastor is amenable, it is possible to be prepared outside of that program.
How to Become a Catholic