在办理医疗器械三类经营许可证时，需要进行以下几个步骤：

完善申请材料：根据相关规定，医疗器械经营者需要准备并提交一系列材料，包括企业的申请表、法人营业执照、医疗器械产品注册证书、产品质量标准、生产和销售质量管理规范等。

提交申请：将完善的申请材料提交给所在地的食品药品监督管理部门。在北京地区，需要将申请材料提交给北京市食品药品监督管理局。申请材料应该按规定的格式和数量递交，确保申请能够顺利进行。

审核和审批：食品药品监督管理部门会对申请材料进行审核，包括对申请者的资质、经营场所、质量管理体系等进行检查。如果申请材料符合要求，且经过现场检查合格，监管部门会进行审批，Zui终决定是否颁发医疗器械三类经营许可证。

Where there are errors in the application materials that can be corrected on the spot, The applicant shall be allowed to make corrections on the spot; if the application materials are incomplete or do not conform to the statutory form, Should inform the applicant on the spot or within five days of all the contents to be corrected, Failure to inform you after the time limit, It shall be accepted from the date of receipt of the application materials; The matters to apply for fall within the scope of the functions and powers of the administrative organ, The application materials are complete and in line with the legal form, Or where the applicant submits all the supplementary and corrected application materials as required by the respective administrative organ, The application for administrative license shall be accepted.