You will need to cancel your retirement visa and apply for a Work permit
You generally cannot combine a Thai Retirement Visa (Non-Immigrant O-A) with investor activities in a business, as it is designed for retirees without work or business obligations. For individuals with investment plans or who want to run a business, the LTR Visa (Long-Term Resident Visa) is the more appropriate option, as it offers specific categories for investors and entrepreneurs with corresponding financial requirements and benefits.