Please drop a Salesforce link into your body details as follows,
//set email content
mail.setSubject('Fill your KYC Details for Verification');
String body = 'Dear ' + cus.Name + ', ';
body += '<br> Please complete your KYC Verification process by filling the details to open your Bank Account.';
body += '<br> https:...
UrlHandling is passed into the MarketingCloudConfig. As such, you must implement it in native code. Examples of this can be seen in the Learning Applications: https://github.com/salesforce-marketingcloud/MarketingCloudSDK-Android/blob/master/app/src/main/java/com/salesforce/marketingcloud/learningapp/BaseLearningApplication.kt#L126