How to find map value present in the string c++ here need to match map value to substring of a string

below are map variables in code.

boardSelectMap.insert(std::pair<std::string, std::string>("boardtype1", "RBCM_CLEO"));
        boardSelectMap.insert(std::pair<std::string, std::string>("boardtype2", "RBCM_AIVI2_C2"));
        boardSelectMap.insert(std::pair<std::string, std::string>("boardtype3", "RBCM_AIVI2_ADR3"));
        boardSelectMap.insert(std::pair<std::string, std::string>("boardtype4", "RBCM_AIVI2_SBR"));
        boardSelectMap.insert(std::pair<std::string, std::string>("boardtype5", "RBCM_AIVI2_C1"));
        boardSelectMap.insert(std::pair<std::string, std::string>("boardtype6", "RBCM_AIVI2_C3"));
        boardSelectMap.insert(std::pair<std::string, std::string>("boardtype7", "RBCM_AIVI2_CCS1_1_B0"));
        boardSelectMap.insert(std::pair<std::string, std::string>("boardtype8", "RBCM_AIVI2_J32V_B0"));

std::string boardFileContent = "as*. RBCM AIVI2 C2*.-3gb board based on r8a7796";

Here i need to find boardSelectMap[boardtype2] or "RBCM_AIVI2_C2" is selected i am not to do it with find()