Add class to only 1 link in menu

Hello in my page https://segnalidiborsa.com/ , in the top menu i want to make yellow only the ‘Telegram’ link.
I thought i could do this by altering the class of this specific item.
So by inspect element i found the class and in custom css i do the following:
.menu-item-6915 {
color:yellow;
}

i even tried with !important, it doesn’t work

Actually, i thought best would be to add a custom class only to this link?
Or exclude it somehow from the inheritance css by using :not but still it requires a custom class.

How do i add a custom class only to this item from the item list of menu?
thanks

I just removed the hover, because i want it always yellow.
Thank you