TMEP § 1306.06(b)
If a certification mark application is filed but the mark is actually another type of mark, or if an application for another type of mark is filed but it is actually a certification mark, the application may be amended to request registration as the proper type of mark. Also, the application should be re-executed because some essential allegations differ for the different types of marks.
For collective mark and certification mark applications that are subject to the base application requirements (see TMEP §819), no additional fee is required if the mark type is amended to another type of mark.
See TMEP §1306.04(d)(i) regarding appearance of a trademark or service mark in a certification mark or on a specimen, §1306.04(b)(ii) regarding related company use, and §1306.04(b)(iii) regarding use under a patent license.