Of course, you cannot empty this table. These data are the "heart" of your site. You just lose everything.

I don't know what's the purpose of your site, but it's all in spam and fake accounts. 

You just need to delete fake accounts with their content and take care that such cases are not in the future.

How can I delete fake and spam accounts ?

Go to https://safalaya.com/admin/users, mark the users you want to delete and click the "delete" button.

After that, install Spam Login Filter and Spam Throttle and adjust the settings accordingly. I would also suggest one of Nikolai's Captcha plugins. I've had 0 fake accounts since I installed hCaptcha.

However, looking at your site, it would probably be easier to delete the whole Elgg installation and start all over again, as you would also have to delete hundreds of Spam entries all over the site. Is there any non-spam content at all that you would want to back up?

https://docs.hcaptcha.com/ is not clear to me how to add the code to my elgg login form ? Please help .

I can't help you with that, no idea. I bought the plugin from Nikolai for hCaptcha, installed the mod and that was it. Easy and fast.