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I solve my problem. Here is the code snipped

        layer->startEditing();
        qDebug()<< "is editable " << layer->isEditable();
        QgsFeatureRenderer * layerRenderer= layer->renderer();
        QgsSingleSymbolRenderer *mSingleRenderer = QgsSingleSymbolRenderer::convertFromRenderer(layerRenderer);
        QgsMarkerSymbol* symbol = new  QgsMarkerSymbol();
        QgsStringMap mp;
       // mp[QString("fill")]= QString("red");
        mp[QString("name")]= QString("food_pub.svg");
        mp[QString("size")]= QString("6");
      //  mp[QString("outline")]=QString("black");
     //   mp[QString("outline-width")]=QString("6.8");

        QgsSvgMarkerSymbolLayer svglayer("C:\\OSGeo4W64\\apps\\qgis-ltr-dev\\svg\\food\\food_pub.svg");
        QgsSymbolLayer* svgsymbol=svglayer.create(mp);
       auto newsym=     symbol->createSimple(mp);
       newsym->changeSymbolLayer(0,svgsymbol);
       mSingleRenderer->setSymbol(newsym);
        layer->setRenderer(mSingleRenderer);
        layer->triggerRepaint();
        layer->commitChanges();
        qDebug()<< "is editable after commiting  " << layer->isEditable();