How do you say you are welcome Mr in spanish?

Many possibilities here depending on context and whether the question meant to use you're instead of your.

Your welcome, kind sir, [was appreciated], .... = Su bienvenida, señor amable, [fue agradecida]

You're welcome [here], kind sir = Bienvenido, amable señor

In response to "Thank you/" You're welcome, kind sir. = De nada, amable señor.

De Nada, literally translates back to: for nothing. Other options would be: A las ordenes (at the orders/at your command--this is the most subservient "you're welcome" and appropriate in a customer/merchant relationship or employer/employee relationship), No hay de que dar gracias (there is nothing to thank me for.)

There is no direct translation to the Word "kind" in this context.

Amable literally translates back as "lovable" but is really closer to kind than anything else.

benévolo (benevolent) or cariñoso (Caring, loving) do not really work here, but could be used.

If you are looking for a formal and subservient "You're welcome, sir", "A las ordenes, Señor" would be appropriate.