"Forwarding" in SMS (texting) means that instead of going to your phone, it'll go to the phone you're forwarding to.
There's no forwarding in the email sense in SMS - just copy the text and paste it into a new message to the new recipient. (Remember, the protocol was designed to send short messages [hence Short Message Service] to pocket pagers.) There may be apps that allow you to forward a conversation, or a block of conversations, to another number or group, but it's not a native function of an SMS app.