MetadataService.apxc

public class MetadataService {
    public static void UpdateCustomMetadata(string token) {
        
        Metadata.CustomMetadata customMetadata =  new Metadata.CustomMetadata();
        customMetadata.fullName = 'GoogleAuthSetting.AccessToken';
        customMetadata.label = 'AccessToken';
        customMetadata.protected_x = true;
        
        Metadata.CustomMetadataValue accessToken = new Metadata.CustomMetadataValue();
        accessToken.field = 'AccessToken__c';
        accessToken.value = token;
        customMetadata.values.add(accessToken);
        
        Metadata.DeployContainer mdContainer = new Metadata.DeployContainer();
        mdContainer.addMetadata(customMetadata);
        CustomMetadataCallback callback = new CustomMetadataCallback();
        Id jobId = Metadata.Operations.enqueueDeployment(mdContainer, callback);
    }
    
    public class CustomMetadataCallback implements Metadata.DeployCallback {
        
        public void handleResult(Metadata.DeployResult result,
                                 Metadata.DeployCallbackContext context) {
                                     if (result.status == Metadata.DeployStatus.Succeeded) {
                                         System.debug(' success : '+ result);
                                     } else {
                                         System.debug(' fail : '+ result);
                                     }
                                 }
    }
}