Please modify this code:
app\code\Bss\ReviewReminder\Observer\ReviewSaveAfter.php:
$emailTemplate = $this->helper->configCouponEmailTemplate($order->getStore()->getCode());

app\code\Bss\ReviewReminder\Helper\Email.php:
try {
$storeId = (isset($templateVar['storeName']) ? $templateVar['storeName']->getId() : 0);
$storeCode = (isset($templateVar['storeName']) ? $templateVar['storeName']->getCode() : 'admin');
$email = $this->helper->configSenderEmail($storeCode);

//Send Email
$transport = $this->transportBuilder
>setTemplateIdentifier($emailTemplate)
->setTemplateOptions(
[
'area' => \Magento\Framework\App\Area::AREA_FRONTEND,
'store' => $storeId,
]
)

app\code\Bss\ReviewReminder\Helper\Data.php:
public function configSenderEmail($storeCode)
{
return $this>scopeConfig->getValue(
'reviewreminder/general/email_sender',
\Magento\Store\Model\ScopeInterface::SCOPE_STORE,
$storeCode
);
}

public function configEmailTemplate($storeCode)
{
return $this->scopeConfig->getValue(
'reviewreminder/general/email_template',
\Magento\Store\Model\ScopeInterface::SCOPE_STORE,
$storeCode
);
}

public function configCouponEmailTemplate($storeCode)
{
return $this->scopeConfig->getValue(
'reviewreminder/coupon/email_template',
\Magento\Store\Model\ScopeInterface::SCOPE_STORE,
$storeCode
);
}

app\code\Bss\ReviewReminder\Cron\SendMailCron.php
$emailTemplate = $this->helper->configEmailTemplate($storeCode);


If you have any question, please let us know.